  United States Court of Appeals
       for the Federal Circuit
                ______________________

     SCA HYGIENE PRODUCTS AKTIEBOLAG
        AND SCA PERSONAL CARE, INC.,
              Plaintiffs-Appellants,

                           v.

    FIRST QUALITY BABY PRODUCTS, LLC,
        FIRST QUALITY HYGIENIC, INC.,
      FIRST QUALITY PRODUCTS, INC. AND
    FIRST QUALITY RETAIL SERVICES, LLC,
              Defendants-Appellees.
             ______________________

                      2013-1564
                ______________________

   Appeal from the United States District Court for the
Western District of Kentucky in No. 10-CV-0122, Chief
Judge Joseph H. McKinley, Jr.
                ______________________

             Decided: September 17, 2014
               ______________________

    MARTIN J. BLACK, Dechert LLP, of Philadelphia,
Pennsylvania, argued for plaintiffs-appellants. With him
on the brief were KEVIN M. FLANNERY and TERI-LYNN A.
EVANS.

   KENNETH P. GEORGE, Amster, Rothstein & Ebenstein,
LLP, of New York, New York, argued for defendants-
2        SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



appellees. With him on the brief were CHARLES R.
MACEDO and MARK BERKOWITZ.
               ______________________

    Before REYNA, WALLACH, and HUGHES, Circuit Judges.
HUGHES, Circuit Judge.
     SCA owns U.S. Patent No. 6,375,646 (the ’646 patent),
which relates to certain adult incontinence products.
After SCA sued a competitor, First Quality, for infringe-
ment of the ’646 patent, the district court dismissed the
case, finding that SCA’s claims were barred by both
laches and equitable estoppel. Because the district court
properly concluded that SCA’s more than six-year delay in
filing suit warranted dismissal based on laches, we affirm
the court’s grant of summary judgment in that regard.
But given SCA and First Quality’s limited interactions,
there remain genuine issues of material fact pertaining to
equitable estoppel. Accordingly, we reverse the district
court’s grant of summary judgment as to equitable estop-
pel and remand for further proceedings consistent with
this opinion.
                                I
    SCA 1 and First Quality 2 compete in the market for
adult incontinence products. On October 31, 2003, SCA
sent a letter to First Quality, suggesting that certain First
Quality products might infringe the ’646 patent. The
letter stated:


     1  SCA refers collectively to plaintiffs-appellants
SCA Hygiene Products Aktiebolag and SCA Personal
Care, Inc.
   2    First Quality refers collectively to defendants-
appellees First Quality Baby Products, LLC; First Quality
Hygienic, Inc.; First Quality Products, Inc.; and First
Quality Retail Services, LLC.
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS    3



       It has come to our attention that you are mak-
   ing, selling and/or offering for sale in the United
   States absorbent pants-type diapers under the
   name Prevail® All NitesTM. We believe that these
   products infringe claims of [the ’646 patent].
       We suggest that you study [the ’646 patent].
   If you are of the opinion that the First Quality
   Prevail® All NitesTM absorbent pants-type diaper
   does not infringe any of the claims of this patent,
   please provide us with an explanation as to why
   you believe the products do not infringe. If you
   believe that the products do infringe, please pro-
   vide us with your assurance that you will imme-
   diately stop making and selling such products.
J.A. 544. First Quality responded on November 21, 2003,
and stated:
       As you suggested, we studied [the ’646 pa-
   tent] . . . . In addition, we made a cursory review
   of prior patents and located U.S. Patent No.
   5,415,649, (“the ‘649 Patent”), which was filed in
   the United States on October 29, 1991 and is
   therefore prior to your client’s ‘646 Patent. A re-
   view of Figs. 3 and 4 of the prior ‘649 Patent re-
   veals the same diaper construction claimed by the
   ‘646 Patent. Thus, the prior ‘649 Patent invali-
   dates your client’s ‘646 Patent. As you know, an
   invalid patent cannot be infringed.
J.A. 547. These two communications were the only in-
stances in which either party mentioned the ’646 patent.
SCA and First Quality exchanged four more brief letters
over the next eight months before ceasing communica-
tions, but those letters concerned a different patent and
different First Quality products.
   On July 7, 2004—one day after SCA sent its final
communication to First Quality—SCA filed an ex parte
4    SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



reexamination request for the ’646 patent. SCA asked the
United States Patent and Trademark Office (PTO) to
review the patentability of the ’646 patent in light of
the ’649 patent and European Patent Application No.
0187727 A2. About three years later, on March 27, 2007,
the PTO confirmed the patentability of all 28 original
claims and issued several new claims added during reex-
amination.
    SCA never notified First Quality about the reexami-
nation proceedings. According to SCA, it believed it was
under no obligation to do so because the PTO provides
public notice of all reexaminations.       See 37 C.F.R.
§§ 1.11(c), 1.570(f). First Quality, meanwhile, stated that
it no longer considered the ’646 patent “to be an issue”
after making its invalidity allegations. SCA Hygiene
Prods. AB v. First Quality Baby Prods., LLC, No. 10-cv-
0122, 2013 WL 3776173, at *10 (W.D. Ky. July 16, 2013)
(internal quotation marks omitted).
    Starting in 2006, while the ’646 patent was under
reexamination, First Quality began expanding its line of
adult incontinence products. In 2008, after the reexami-
nation had concluded, First Quality acquired Covidian’s
Tyco Healthcare Retail Group LP and, along with it, some
of the products at issue in this case. It continued its
expansion in 2009 at a cost of more than $10 million.
    SCA claims that it began preparing to file suit against
First Quality immediately after the reexamination certifi-
cate issued in March 2007. But SCA did not file suit or
otherwise contact First Quality until August 2, 2010,
when it filed its complaint in this case—about six years
and nine months after SCA first contacted First Quality
about the ’646 patent. According to SCA, it spent more
than three years after the reexamination concluded
implementing new business management structures,
evaluating outside counsel, and examining potentially
infringing products on the market.
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS      5



    First Quality counterclaimed for declaratory judg-
ments of noninfringement and invalidity. After the
district court’s claim construction order, First Quality
moved for partial summary judgment of noninfringement
and for summary judgment of laches and equitable estop-
pel. The district court granted First Quality’s motion for
summary judgment as to laches and equitable estoppel
and dismissed the remaining motion as moot.
    SCA appeals. We have jurisdiction under 28 U.S.C.
§ 1295(a)(1).
                             II
                             A
     Laches is an equitable defense to patent infringement
that may arise only when an accused infringer proves by a
preponderance of evidence that a patentee (1) unreasona-
bly and inexcusably delayed filing an infringement suit
(2) to the material prejudice of the accused infringer. A.C.
Aukerman Co. v. R.L. Chaides Constr. Co., 960 F.2d 1020,
1028–29, 1045 (Fed. Cir. 1992) (en banc). If these prereq-
uisite elements are present, a court must then balance
“all pertinent facts and equities,” including “the length of
delay, the seriousness of prejudice, the reasonableness of
excuses, and the defendant’s conduct or culpability” before
granting relief. Id. at 1034. When found, laches bars
retrospective relief for damages accrued prior to filing suit
but does not bar prospective relief. Id. at 1041.
     Delays exceeding six years give rise to a presumption
that the delay is unreasonable, inexcusable, and prejudi-
cial. Wanlass v. Gen. Elec. Co., 148 F.3d 1334, 1337 (Fed.
Cir. 1998). Under this presumption, the burden of evi-
dentiary production shifts from the accused infringer to
the patentee. Id.; see also Fed. R. Evid. 301; Aukerman,
960 F.2d at 1035–36. Both of these presumptions disap-
pear if the patentee can identify evidence sufficient for a
reasonable jury to conclude either that the delay was
6     SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



excusable or not unreasonable, or that it was not materi-
ally prejudicial. See Wanlass, 148 F.3d at 1337. If the
patentee meets this burden of production, the accused
infringer must prove both elements of laches by a prepon-
derance of evidence. Aukerman, 960 F.2d at 1045.
                             B
     Equitable estoppel may only arise when an accused
infringer shows by a preponderance of evidence that (1) a
patentee, acting on the basis of accurate facts, communi-
cated something in a misleading way, by words, conduct,
or omission, to an alleged infringer, (2) on which the
accused infringer relied, (3) such that he would be mate-
rially prejudiced if the patentee is allowed to assert a
claim that is inconsistent with his earlier communication.
See id. at 1041, 1046. But “even where the three elements
of equitable estoppel are established, [a court must] take
into consideration any other evidence and facts respecting
the equities of the parities in exercising its discretion and
deciding whether to allow the defense.” Id. at 1043.
When found, equitable estoppel acts as a complete bar to
a patentee’s infringement claim. Id. at 1041.
     Although an equitable estoppel defense may appear
similar to a laches defense when a patentee has delayed
filing suit, the two defenses are distinct. For example,
unlike laches, equitable estoppel requires that a “plain-
tiff’s inaction . . . be combined with other facts respecting
the relationship or contacts between the parties to give
rise to the necessary inference that the claim against the
defendant is abandoned.” Id. at 1042. Moreover, equita-
ble estoppel requires that the defendant rely, to its detri-
ment, on the patentee’s abandonment. See id. at 1042–43.
See also Meyers v. Asics Corp., 974 F.2d 1304, 1308 & n.1
(Fed. Cir. 1992). And a court may not presume that the
underlying elements of equitable estoppel are present,
regardless of how much time has passed. Aukerman, 960
F.2d at 1043.
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS     7



                             C
    The conclusion as to whether laches or equitable es-
toppel has been established is “committed to the sound
discretion of the trial judge.” Id. at 1028. Accordingly, we
review conclusions about laches and equitable estoppel for
abuse of discretion. Id.
    But “[l]aches is not established by undue delay and
prejudice. Those factors merely lay the foundation for the
trial court’s exercise of discretion.” Id. at 1036. These
two foundational inquiries are questions of fact. See id. at
1035 (referring to them as “the underlying factual ele-
ments” of laches); id. at 1038 (referring to “either factual
element of a laches defense”); Hemstreet v. Computer
Entry Sys. Corp., 972 F.2d 1290, 1292 (Fed. Cir. 1992)
(“[Laches] ultimately turn[s] on underlying factual deter-
minations.”). Similarly, the prerequisites of equitable
estoppel are “factual elements . . . on which the discre-
tionary power of the court rests.” Aukerman, 960 F.2d at
1043.
    Because the underlying elements of laches and equi-
table estoppel are questions of fact, we review ultimate
findings as to those elements for clear error. See Fed. R.
Civ. P. 52(a)(6); Knowles v. Mirzayance, 556 U.S. 111, 126
(2009); Sea Byte, Inc. v. Hudson Marine Mgmt. Servs.,
Inc., 565 F.3d 1293, 1304 (11th Cir. 2009). After a grant
of summary judgment, however, we review the underlying
factual elements de novo 3 to determine whether any




   3    We review this aspect of a court’s summary judg-
ment award under regional circuit law. Sedarevic v.
Advanced Med. Optics, Inc., 532 F.3d 1352, 1362 (Fed.
Cir. 2008). In this case, the Sixth Circuit’s de novo stand-
ard applies. See Mazur v. Young, 507 F.3d 1013, 1016
(6th Cir. 2007).
8     SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



genuine issues of material fact remain. Fed. R. Civ. P.
56(a); see also Wanlass, 148 F.3d at 1337.
    When a trial court mistakenly concludes that the fac-
tual elements of laches or equitable estoppel have been
established and grants relief, such error constitutes an
abuse of discretion in the ultimate judgment. See Auker-
man, 960 F.2d at 1039; Heat & Control, Inc. v. Hester
Indus., Inc., 785 F.2d 1017, 1022 (Fed. Cir. 1986) (“An
abuse of discretion occurs when . . . the decision is based
on an erroneous conclusion of law . . . [or] the court’s
findings are clearly erroneous.”). But if such error is
absent, a trial court’s grant of laches or equitable estoppel
can be overturned only if it represents unreasonable
judgment in weighing all pertinent facts and equities. See
Aukerman, 960 F.2d at 1039, 1043; cf. Digital Control,
Inc. v. Charles Mach. Works, 437 F.3d 1309, 1313 (Fed.
Cir. 2006) (describing a similar fact/equity hybrid stand-
ard of review for inequitable conduct).
                             III
    We first turn to the issue of laches. As a preliminary
matter, SCA argues that Petrella v. Metro-Goldwyn-
Mayer, Inc., 134 S. Ct. 1962 (2014), “compels a finding
that [Aukerman] is no longer good law.” Notice of Sup-
plemental Authority at 2, SCA Hygiene Prods. AB v. First
Quality Baby Prods., No. 2013-1564 (Fed. Cir. May 27,
2014), ECF No. 51. In particular, SCA points out that the
Supreme Court has never “approved the application of
laches to bar a claim for damages brought within the time
allowed by a federal statute of limitations.” Petrella, 134
S. Ct. at 1974.
    But Petrella notably left Aukerman intact. See id. at
1974 n.15 (“We have not had occasion to review the Fed-
eral Circuit’s position.”). Because Aukerman may only be
overruled by the Supreme Court or an en banc panel of
this court, Aukerman remains controlling precedent. See,
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS      9



e.g., Tate Access Floors, Inc. v. Interface Architectural
Res., Inc., 279 F.3d 1357, 1366 (Fed. Cir. 2002).
                             A
    SCA argues that the reexamination proceedings pre-
clude application of the laches presumptions in this case
because the reexamination period should be excluded
from the total delay. The district court rejected that
theory. In its view, because SCA filed suit more than six
years after first learning of First Quality’s allegedly
infringing activities, the laches presumptions applied. We
agree.
    Whether SCA’s delay was excusable relates to the
question of whether it can rebut the presumption of
unreasonable and inexcusable delay, not whether the
presumption applies in the first place. 4 Because more
than six years elapsed between the time SCA first learned
of First Quality’s allegedly infringing activities and the
time SCA filed infringement claims directed to those
activities, the district court properly found that the laches
presumptions applied.
    Accordingly, summary judgment was appropriate only
if no reasonable jury could have concluded that SCA’s
delay was reasonable, excusable, or materially prejudicial.
See, e.g., Wanlass v. Fedders Corp., 145 F.3d 1461, 1463


    4   A number of cases suggest that a reasonable ex-
cuse may “toll” certain portions of the delay period for
purposes of laches. But these cases are better understood
as analyzing whether the purported justifications excuse
the delay period. See, e.g., Sedarevic, 532 F.3d at 1359;
Meyers v. Brooks Shoe Inc., 912 F.2d 1459, 1462 (Fed. Cir.
1990), overruled on other grounds by Aukerman, 960 F.2d
at 1038–39; Hottel Corp. v. Seaman Corp., 833 F.2d 1570,
1572–73 (Fed. Cir. 1987), overruled on other grounds by
Aukerman, 960 F.2d at 1038–39.
10    SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



(Fed. Cir. 1998). We review this question under the Sixth
Circuit’s de novo standard. See Mazur v. Young, 507 F.3d
1013, 1016 (6th Cir. 2007). If no genuine issues of mate-
rial fact remain, we must also review the district court’s
ultimate decision to grant or deny summary judgment for
abuse of discretion. Gasser Chair Co. v. Infanti Chair
Mfg. Corp., 60 F.3d 770, 773 (Fed. Cir. 1995); Aukerman,
960 F.2d at 1039.
                             1
    Reasonable explanations for delay include attempts to
enforce the patent, such as filing suit against another
infringer or participating in post-grant PTO proceedings.
See Vaupel Textilmaschinen KG v. Meccanica Euro Italia
S.P.A., 944 F.2d 870, 876–78 (Fed. Cir. 1991). SCA as-
serts that the ’646 patent reexamination proceedings
provide a reasonable excuse for its delay in filing suit
against First Quality.
    The district court disagreed. It concluded that “SCA’s
stated reasons for delay in filing suit are legally insuffi-
cient to overcome the presumption of unreasonable delay.”
SCA Hygiene, 2013 WL 3776173, at *6. First, the court
reasoned that, “[u]nder the facts of this case, notice by
SCA of an intent to sue after the reexamination was
required.” Id. at *5. Second, the court “reject[ed] SCA’s
argument that it needed more than three years . . . to
bring infringement claims against First Quality” following
the reexamination. Id. Although we disagree that SCA
was required to provide explicit notice of the reexamina-
tion proceedings to First Quality on the facts of this case,
we nevertheless agree that SCA failed to rebut the pre-
sumption of unreasonable delay.
    A patentee is not required in all cases to provide no-
tice of related proceedings involving the asserted patent
to show its delay was not unreasonable. Aukerman, 960
F.2d at 1039. For example, “[i]f a defendant is . . . aware
of the [proceedings] from other sources, it would place
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS    11



form over substance to require a specific notice.” Id.
Here, the PTO provided public notice of the reexamina-
tion proceedings on August 24, 2004. First Quality could
have learned of those proceedings based on SCA’s initial
notice of the ’646 patent, coupled with the PTO’s subse-
quent notice of the reexamination. Under such circum-
stances, SCA was not required to provide notice of the
reexamination to First Quality.
    But even though SCA’s delay during reexamination
may have been excusable when viewed in isolation, we
must examine whether SCA’s delay, viewed as a whole,
was excusable. The district court found that “SCA admit-
ted that it has continuously tracked First Quality’s activi-
ty since 2003 and has an entire department dedicated
solely to competitive intelligence.” SCA Hygiene, 2013
WL 3776173, at *5. SCA then continued to evaluate First
Quality’s products during the reexamination period. SCA
was also represented by U.S. patent counsel when it sent
letters to First Quality in 2003 and 2004 and during the
reexamination proceedings between 2004 and 2007. Id.
No evidence suggests that SCA was unable to find counsel
or reinitiate contact with First Quality shortly after the
reexamination ended. Moreover, “personal lack of famili-
arity with the patent system . . . does not ex-
cuse . . . failure to file suit.” Sedarevic v. Advanced Med.
Optics, Inc., 532 F.3d 1352, 1360 (Fed. Cir. 2008).
    Given the circumstances, SCA should have been pre-
pared to reassert its rights against First Quality shortly
after the ’646 patent emerged from reexamination. See
Wanlass, 148 F.3d at 1338 (“The availability of delay
based on constructive knowledge of the alleged infringer’s
activities imposes on patentees the duty to police their
rights.”); 6A Donald S. Chisum, Chisum on Patents
§ 19.05[2][a][iii] (2013) (“Many decisions in finding delay
excused emphasize that the patent owner promptly filed
suit after the excuse (such as other litigation) ceased.”).
12       SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



But SCA remained silent for more than three years after
the patent came out of reexamination.
    Accordingly, SCA has failed to raise a genuine issue of
material fact regarding the reasonability of its delay.
Viewing all of the facts in the light most favorable to SCA,
no reasonable fact-finder could conclude that SCA’s delay,
viewed as a whole, was reasonable.
                                2
     There are two categories of prejudice in laches—
evidentiary and economic. Aukerman, 960 F.2d at 1033.
Evidentiary prejudice results when the patentee’s delay
hinders an accused infringer from defending against the
patent suit. This may include, for example, the death of a
critical witness, the dimming of memories, or the loss of
documents. Id. “Economic prejudice may arise where a
defendant and possibly others will suffer the loss of mone-
tary investments or incur damages which likely would
have been prevented by earlier suit.” 5 Id.
    Economic prejudice cannot be attributed to losses
merely associated with a finding of liability for infringe-
ment. Id. Rather, “[t]he courts must look for a change in
the economic position of the alleged infringer during the
period of delay.” Id. For example, “[m]aking heavy
capital investment and increasing production can consti-
tute [economic] prejudice.” Adelberg Labs., Inc. v. Miles,
Inc., 921 F.2d 1267, 1272 (Fed. Cir. 1990). But there
must be a demonstrable nexus between the alleged eco-
nomic prejudice and the patentee’s delay. See, e.g., Hem-


     5  Because the district court was silent as to eviden-
tiary prejudice and because the parties do not contest that
issue here, we must assume there is no genuine factual
dispute that First Quality did not suffer evidentiary
prejudice. We therefore limit our discussion to economic
prejudice.
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS   13



street, 972 F.2d at 1293–94 (“It is not enough that the
alleged infringer changed his position—i.e., invested in
production of the allegedly infringing device. The change
must be because of and as a result of the delay, not simply
a business decision to capitalize on a market opportuni-
ty.”).
    This nexus requirement does not, however, require re-
liance on the patentee’s delay. Asics, 974 F.2d at 1308
n.1. “[T]he question is whether . . . prejudice resulted
from [the] delay,” id. at 1308, and “there is a difference
between prejudice that results from delay and prejudice
that is due to reliance upon delay,” id. at 1308 n.1. Eco-
nomic prejudice results from a patentee’s delay if the
financial losses at issue “likely would have been prevent-
ed by earlier suit.” Aukerman, 960 F.2d at 1033; accord
State Contracting & Eng’g Corp. v. Condotte Am., Inc.,
346 F.3d 1057, 1066 (Fed. Cir. 2003); Gasser Chair, 60
F.3d at 775; Asics, 974 F.2d at 1307–08.
    Here, the district court concluded that SCA failed to
rebut the presumption that First Quality suffered eco-
nomic harm, and we agree. First Quality made a number
of capital expenditures to expand its relevant product
lines and to increase its production capacity. The record
evidence suggests that First Quality would have restruc-
tured its activities to minimize infringement liability if
SCA had brought suit earlier.
     SCA challenges this evidence by asserting that “[t]he
District Court committed reversible error when it credited
the self-serving, uncorroborated testimony of First Quali-
ty’s witness, who was an in-house lawyer and not even a
business person.” Appellants’ Br. 32. SCA is correct, of
course, that the district court was not permitted to assess
the credibility of First Quality’s witnesses on summary
judgment. See Anderson v. Liberty Lobby, Inc., 477 U.S.
242, 255 (1986). But SCA may not rely solely on plead-
ings and speculation to create a genuine issue of material
14    SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



fact; it must identify particular evidence that creates such
a dispute. See Fed. R. Civ. P. 56(c)(1); Matsushita Elec.
Indus. v. Zenith Radio Corp., 475 U.S. 574, 587–88 (1986);
Shreve v. Franklin Cnty., 743 F.3d 126, 132 (6th Cir.
2014).
     SCA has not identified sufficient evidence relevant to
this issue. SCA notes that First Quality considered its
protective underwear business to be important and that
its initiatives in that market were highly successful. SCA
also relies heavily on a statement by First Quality’s
President, Mr. Damaghi, that “after sending [the Novem-
ber 21, 2003] letter this matter was never thought of
again.” J.A. 1171–72. Thus, SCA contends that “First
Quality was motivated by a huge market opportunity and
would have continued to grow its protective underwear
business regardless of when SCA filed suit.” Appellants’
Br. 35–36.
    But Mr. Damaghi’s statement that “this matter was
never thought of again” does not suggest that First Quali-
ty planned to ignore the issue whether or not SCA filed
suit. See SCA Hygiene, 2013 WL 3776173, at *10 (“[W]e
never heard back from [SCA], and as a result we did not
consider it to be an issue because we did not know what, if
any, issue existed for us to follow up on.” (internal quota-
tion marks omitted)). Moreover, there is no dispute that
First Quality considered its protective underwear busi-
ness to be important and that its initiatives in that mar-
ket were highly successful. To suggest, based on this
evidence alone, that First Quality would have continued
its allegedly infringing activities regardless of when or
whether SCA filed suit is pure speculation.
    SCA has not identified any evidence that raises a
genuine issue of material fact regarding First Quality’s
presumed economic prejudice.
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS     15



                             B
     SCA further contends that, even if it failed to rebut
the laches presumptions, “it was an abuse of discretion for
the District Court to refuse to consider the equities fully.”
Appellants’ Br. 52. We agree that the district court
should have evaluated the equities. The court seemed to
treat laches as though relief was automatic so long as
First Quality established the factual prerequisites of the
defense. See SCA Hygiene, 2013 WL 3776173, at *3 (“If
these factors are proven, laches bars the recovery of
patent damages for any time period before the suit was
filed.” (internal quotation marks omitted)). Our law
makes clear, however, that courts should grant relief for
laches only after balancing “all pertinent facts and equi-
ties,” including “the length of delay, the seriousness of
prejudice, the reasonableness of excuses, and the defend-
ant’s conduct or culpability.” Aukerman, 960 F.2d at
1034; see also Gasser Chair, 60 F.3d at 773, 775–76.
    SCA points to (1) its alleged good faith in seeking
reexamination of the ’646 patent, (2) the PTO’s public
notice of the reexamination proceedings, and (3) the fact
that the PTO granted new claims during reexamination.
None of these factors, however, suggest that the district
court’s decision to grant summary judgment of laches
constituted an abuse of discretion. The district court’s
failure to explicitly balance the equities in its decision
was therefore harmless error. See, e.g., Metabolite Labs.,
Inc. v. Lab. Corp. of Am. Holdings, 370 F.3d 1354, 1371
(Fed. Cir. 2004).
                             C
     SCA argues for the first time on appeal that the dis-
trict court erred by applying laches to the new claims
issued during reexamination and to SCA’s allegations
against products introduced after 2008. As a general rule,
“a federal appellate court does not consider an issue not
passed upon below.” Singleton v. Wulff, 428 U.S. 106, 120
16    SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



(1976); see also Golden Bridge Tech., Inc. v. Nokia, Inc.,
527 F.3d 1318, 1322–23 (Fed. Cir. 2008). Because SCA
did not raise these issues in the district court and the
district court did not rule on them, we do not consider
them on appeal.
                             IV
    We next turn to the issue of equitable estoppel and
review de novo whether genuine issues of material fact
remain as to the prerequisite elements. See Fed. R. Civ.
P. 56(a); Celotex, 477 U.S. at 322; Mazur, 507 F.3d at
1016. Because there are no evidentiary burden-shifting
presumptions in equitable estoppel, see Aukerman, 960
F.2d at 1028, 1043, First Quality possessed the burden of
production.
                             A
    The first element of equitable estoppel requires SCA
to have made a misleading communication, either affirm-
atively or by omission, to First Quality. The district court
ruled that “SCA unquestionably misled First Quality
though [sic] its 2003 letter and subsequent inaction.”
SCA Hygiene, 2013 WL 3776173, at *9. The court focused
on SCA’s failure to respond to First Quality’s letter ad-
dressing the ’646 patent and on SCA’s decision to write
First Quality regarding different products and a different
patent. In the court’s view, “[w]hether this letter ‘is
viewed as a tacit withdrawal of the [‘646 patent] or as
misleading silence with respect to the [‘646 patent], the
result is the same, for it was reasonable for [First Quality]
to infer that [SCA] was not continuing the accusation of
infringement as to the [‘646 patent].’” Id. (alterations in
original) (quoting Aspex Eyewear Inc. v. Clariti Eyewear,
Inc., 605 F.3d 1305, 1311 (Fed. Cir. 2010)). We disagree.
    “[S]ilence alone will not create an estoppel unless
there was a clear duty to speak or somehow the patentee’s
continued silence reenforces the defendant’s inference
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS    17



from the plaintiff’s known acquiescence that the defend-
ant will be unmolested.” Aukerman, 960 F.2d at 1043–44
(citations omitted); see also Asics, 974 F.2d at 1308–09.
Although the most common example of equitable estoppel
is a patentee who objects to allegedly infringing activities
and then remains silent for a number of years, that
silence must be “coupled with other factors, [such that
the] patentee’s ‘misleading conduct’ is essentially mislead-
ing inaction.” Aukerman, 960 F.2d at 1042 (emphasis
added); see also Hemstreet, 972 F.2d at 1295; Asics, 974
F.2d at 1308–09.
    For example, in Scholle Corp. v. Blackhawk Molding
Co., 133 F.3d 1469 (Fed. Cir. 1998), the parties had been
engaged in patent litigation over an older product. The
accused infringer later informed the patentee that it
planned to begin marketing a design-around product and
stated that it “would consider the new product non-
infringing unless [the patentee] advised . . . otherwise.”
Id. at 1470. The accused infringer sent samples of the
new product to the patentee and sought its opinion, but
the patentee never responded. During the three years
that followed, the parties discussed the asserted patent at
numerous meetings between high-level officials. Id. at
1470–71. A possible merger was even discussed. Id. at
1471. But, throughout that time, the patentee never
suggested that it thought the accused infringer’s new
product line infringed. Id. The patentee only offered
opinions about the older product line. Under those cir-
cumstances, we held that the parties’ course of dealings
was such that the patentee’s silence amounted to mislead-
ing inaction. Id. at 1472.
    Similarly, in Aspex—an opinion on which the district
court relied heavily—the parties had been embroiled in a
related patent litigation in the past. 605 F.3d at 1308.
The accused infringer later began marketing a redesigned
product similar to those that had been litigated, and the
patentee threatened “to fully and vigorously enforce [its]
18    SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



rights” under four related patents. Id. (internal quotation
marks omitted). In response, the accused infringer re-
quested specific infringement contentions, but the patent-
ee complied regarding only two of the patents. It made no
reference to the other two. After three years of silence,
the patentee renewed its objections with respect to one of
the two patents for which it declined to provide specific
infringement contentions. Under those circumstances,
this court stated that “[w]hether this sequence is fairly
viewed as a tacit withdrawal of the . . . patent, or as
misleading silence with respect to the . . . patent, the
result is the same, for it was reasonable . . . to infer that
[the patentee] was not continuing the accusation of in-
fringement.” Id. at 1311.
    Compared to Scholle and Aspex, the interaction be-
tween SCA and First Quality reflected in the record is
meager. SCA and First Quality exchanged only six terse
letters over a course of eight months. And only two of
those letters, sent within one month of one another,
referenced the ’646 patent or the accused products.
Unlike in Aspex and Scholle, First Quality never solicited
further comment from SCA. Thus, a reasonable juror
may be less likely to infer that SCA’s subsequent silence
misled First Quality. Moreover, the record does not
suggest that the parties engaged in serious discussions
involving the accused products or any related patent, let
alone the ’646 patent. Nor does the record suggest that
SCA and First Quality had been adversaries in prior
related litigations or that they held any other close rela-
tionship.
     Nevertheless, First Quality maintains that SCA’s si-
lence was tantamount to an admission that the ’646
patent was invalid. But “a mere verbal charge of in-
fringement, if made, followed by silence [i]s not sufficient
affirmative conduct to induce a belief that [the patentee]
ha[s] abandoned an infringement claim.”          Meyers v.
Brooks Shoe, Inc., 912 F.2d 1459, 1462 (Fed. Cir. 1990),
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS     19



overruled on other grounds by Aukerman, 960 F.2d at
1038–39. Here, SCA almost immediately filed a request
for ex parte reexamination of the ’646 patent to address
the issues raised by First Quality—an action that could
reasonably be viewed as inconsistent with SCA’s alleged
acquiescence. Thus, record evidence supports a version of
events that differs from First Quality’s. A reasonable
juror could conclude that First Quality raised an issue
SCA had overlooked and that SCA, rather than acquiesc-
ing, took immediate action.
    To justify summary judgment of equitable estoppel,
any inference that a patentee made a misleading commu-
nication by omission or acquiescence “must be the only
possible inference from the evidence.” Aukerman, 960
F.2d at 1044. That is not the case here. Accordingly,
genuine issues of material fact remain as to whether SCA
made a misleading communication to First Quality.
                             B
    Equitable estoppel also requires that material preju-
dice to the accused infringer be caused by his reliance on
the patentee’s misleading communication. Id. at 1028,
1041–42. In this case, the district court found that no
genuine issue of material fact remained with regard to
First Quality’s reliance. In its view, the testimonies of
Messrs. Oppenheim and Damaghi conclusively estab-
lished First Quality’s reliance.
    There is a difference between prejudice that results
from a patentee’s alleged misrepresentation and prejudice
caused by reliance upon it. Asics, 974 F.2d at 1308 n.1.
Although the former is sufficient to show a nexus for
laches, the latter is required to show reliance for equitable
estoppel. Id. As Aukerman explained, “[t]he accused
infringer must show that, in fact, it substantially relied
on the misleading conduct of the patentee in connection
with taking some action.” 960 F.2d at 1042–43.
20   SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS



    In this case, Mr. Damaghi testified that “after sending
[the November 21, 2003] letter this matter was never
thought of again.” J.A. 1171–72. Although this testimony
demonstrates that First Quality disregarded SCA’s alle-
gations involving the ’646 patent, it does not necessarily
establish that First Quality made capital investments and
expanded its business in connection with SCA’s subse-
quent silence. Mr. Damaghi’s testimony acknowledges
the possibility that some issues regarding the ’646 patent
may not have been fully resolved. See SCA Hygiene, 2013
WL 3776173, at *10 (“[W]e did not consider it to be an
issue because we did not know what, if any, issue existed
for us to follow up on.” (internal quotation marks omit-
ted)). And even the most rudimentary due diligence by
First Quality would have revealed that SCA had filed a
reexamination request for the ’646 patent. Thus, a rea-
sonable juror could conclude that First Quality’s reliance,
to the extent it can be established, was not reasonable.
    Mr. Oppenheim’s testimony also fails to establish
First Quality’s reliance. As in-house counsel, he testified
that First Quality would not have made certain capital
investments had it been involved in an earlier lawsuit
over those products. Although that may show a nexus for
purposes of laches, it does not necessarily establish that
First Quality expanded its business after considering the
implications of SCA’s silence.
    Accordingly, genuine issues of material fact remain as
to whether First Quality relied on its own opinion that
the ’646 patent was invalid (or simply ignored the ’646
patent), rather than relying on SCA’s silence. See Gasser
Chair, 60 F.3d at 776 (reversing a judgment of equitable
estoppel because the accused infringer “believed the
patent was invalid” and “paid little attention to [the
patentee’s] complaints”); Hemstreet, 972 F.2d at 1294–95
(reversing a judgment of equitable estoppel because of a
complete absence of evidence that the accused infringer’s
SCA HYGIENE PRODUCTS   v. FIRST QUALITY BABY PRODUCTS   21



actions “were in reliance upon supposed actions of [the
patentee], rather than a business judgment of its own”). 6
                             V
    We have considered the parties’ remaining arguments
and find them unpersuasive. Accordingly, we affirm the
district court’s grant of summary judgment as to laches,
reverse its grant of summary judgment as to equitable
estoppel, and remand for further proceedings consistent
with this opinion.
 AFFIRMED-IN-PART, REVERSED-IN-PART, AND
               REMANDED
   No costs.




   6   Having decided that issues of material fact re-
main as to the other elements of the equitable estoppel
defense, we do not address whether First Quality suffered
material prejudice. The district court may consider this
element further on remand.
