Why are chemical patent claims so difficult to understand? This was the question posed during a 1961 presentation before the Division of Chemical Literature for the American Chemical Society. According to the author, “[A]ttention has been called to the ‘sometimes baffling’ and seemingly ‘absurd’ idiom in which are cast chemical patent claims.”1 At least some of the blame for the confusion was attributed by the author to the “so-called ‘Markush’ claim.”2 Thus, the author wisely advised, “[A]n understanding of the philosophy behind the Markush expression in chemical claims might help to understand better the meaning of chemical claims themselves.”3 More than fifty years later, and at a time where subject matter eligibility, written description, and definiteness issues are at the forefront of the patent prosecution sphere, the Federal Circuit’s decision in Multilayer Stretch Cling Film Holdings, Inc. v. Berry Plastics Corp., Nos. 2015-1420, -1477 (Fed. Cir. Aug. 4, 2016), revisits the Markush claims and offers guidance on their proper use.

In Ex parte Markush, 1925 C.D. 126 (Comm’r Pat. 1924), the Commissioner of Patents held that “where no generic expression exists by which a group of alternative elements can be claimed applicants are permitted to recite the elements in the alternative.” Thus, “[a] Markush claim is a particular kind of patent claim that lists alternative species or elements that can be selected as part of the claimed invention.” Multilayer Stretch, slip op. at 10. Although the concept can be extended to various technologies, traditionally, Markush claims have been more prevalent in the chemical arts, where a Markush claim often recites the presence of a specific substituent selected from a recited group of chemicals.

No precise linguistic formula is required to create a Markush claim. See, e.g., id. The guidelines for patent examination are instructive on this point, providing that the ‘[a]lternative expressions are permitted’ so long as the claim ‘recites a list of alternatively useable species’ with no ‘uncertainty or ambiguity with respect to the question of scope or clarity of the claims.’ Id. (alteration in original) (quoting MPEP § 2173.05(h)). The Federal Circuit has also explained that “[a] Markush group, incorporated in a claim, should be ‘closed,’ i.e. it must be characterized with the transition phrase ‘consisting of,’ rather than ‘comprising’ or ‘including.’” Abbott Labs. v. Baxter Pharm. Prods., Inc., 334 F.3d 1274, 1280-81 (Fed. Cir. 2003) (alteration in original) (citation omitted)). In Multilayer Stretch, the Federal Circuit addressed the proper scope of Markush claims by looking at two different ways in which the term “consisting of” was used in the claims at issue.

At issue in the case were patent claims directed to multilayered thermoplastic stretch wrap films. In particular, the Federal Circuit was asked to weigh in on the proper construction of clause (b) of independent claim 1 and similarly worded independent claim 28. Claim 1 is representative: “(b) five identifiable inner layers, with each layer being selected from the group consisting of linear low density polyethylene [LLDPE], very low density polyethylene [VLDPE], ultra low density polyethylene [ULDPE], and metallocene-catalyzed linear low density polyethylene [mLDPPE] resins; said resins are homopolymers, copolymers, or terpolymers, of ethylene and C3 to C20 alpha-olefins....” Dependent claim 10, which recites, in relevant part, “[t]he multi-layer, thermoplastic stretch wrap film of claim 1, where at least one said inner layer comprises low density polyethylene homopolymers [LDPE],” was also addressed.

Element (b) essentially creates a Markush group that lists four species or types of resin—LLDPE, VLDPE, ULDPE, and mLLDPE—understood to be alternately useable as “inner layers” of the claimed film. The district court construed the claim to require that each of the five layers of the film be composed of only one of the four listed resins (i.e., excluding layers made of blends of the recited resins). Id. at 2. Following this construction, the district court granted summary judgment of noninfringement, as at least one inner layer of the accused films contained blends of resins from the class of mLLDPE, ULDPE, and LLDPE, a fact that both parties agreed on. See id. at 8. The district court further invalidated claim 1, finding that it was closed to resins other than the ones explicitly recited in the Markush group. In addressing the issue of claim construction, the Federal Circuit dealt with two issues: (1) whether the Markush group of element (b) is closed to resins other than the listed four, and (2) whether the Markush group is closed to blends of the four listed resins. Id. at 11. In short, the Federal Circuit answered “yes” to the first question (over the dissent of Judge Taranto) and “no” to the second question.

On the first issue, the Federal Circuit reiterated that the use of the transitional phrase “consisting of” to set off a patent claim element creates a very strong presumption that the claim element is “closed” and therefore “exclude[s] any elements, steps, or ingredients not specified in the claim.” Id. at 12 (alteration in original) (quoting AFG Indus., Inc. v. Cardinal IG Co., 239 F.3d 1239, 1245 (Fed. Cir. 2001)).. “‘[I]t is not inconceivable that a patentee could break with conventional claim construction and become his own lexicographer,’ so as to give [the term] ‘consisting of’ an alternative, less restrictive meaning.” Id. (quoting Conoco, Inc., v. Energy & Envtl. Int’l, L.C., 460 F.3d 1349, 1359 n.4 (Fed. Cir. 2006). “But to overcome the exceptionally strong presumption that a claim term set off with ‘consisting of’ is closed to unrecited elements, the specification and prosecution history must unmistakably manifest an alternative meaning.” Id.

Multilayer argued that this alternative meaning was communicated in the patent. But rather than arguing that the specification of the patent indeed had an unmistakable intent to open element (b) to any unrecited resin, Multilayer’s argument was more focused. In particular, Multilayer argued that the claimed inner layers should be open to one resin specifically claimed in its dependent claims (i.e., low density polyethylene (LDPE)). Id. at 14-15. A closed interpretation of claim 1, Multilayer argued, would be improper as the Court should “strive[ ] to reach a claim construction that does not render claim language in dependent claims meaningless.” Id. at 16 (alteration in original) (quoting Ortho-McNeil Pharm., Inc. v. Mylan Labs., Inc., 520 F.3d 1358, 1362 (Fed. Cir. 2008)). The court rejected Multilayer’s position, noting that while dependent claims can provide guidance in the proper interpretation of the scope of an independent claim, “[t]he dependent claim tail cannot wag the independent claim dog.” Id. (quoting N. Am. Vaccine, Inc. v. Am. Cyanamid Co., 7 F.3d 1571, 1577 (Fed. Cir. 1993)).

Consistently, the court found that the specification did not provide “a clear intent to open the Markush group of element (b) to LDPE or to any other resin not expressly listed in the claim.” Id. at 15. With this finding, the dependent claims that claim inner films with resins other than those four recited in claim 1, including LDPE, also were held invalid.

Dissenting, Judge Taranto focused on the fact that the language in the claim was not a classic Markush claim, as the term preceding the listing was not representative of the generic type of elements recited within the group. In particular, Judge Taranto argued that a “layer” is an open-ended physical structure that does not “have to be one or more of the listed species” of resins. Taranto Dissent at 4. If the claim had said “layer consisting of” one or more of the listed resins, Judge Taranto explained, the meaning would have been plain, as it would have conveyed that the layer must be made out of only the listed resins, and not others. Id. at 2-3. However, the language actually used in the claims is a step removed. In element (b), “consisting of” does not follow and directly modify “layer”; it follows and directly modifies “group.” Id. at 2. Thus, the phrase characterizes the relationship between “group” and the listed resins: the latter are all the members of the former. Id. It does not characterize the (closed or open) relationship between “layer” and what materials can be ingredients of the layer. Id. The claim phrase naming that relationship is “selected from,” not “consisting of.” Id. at 2-3. The established meaning of “consisting of” therefore does not determine the meaning of the claim language here. Id at 3.

On the second question, i.e., whether limitation (b) of claims 1 and 28 is closed to blends of LLDPE, VLDPE, ULDPE, and mLLDPE, the Federal Circuit agreed with Multilayer that the Markush group of element (b) must be construed to permit blends of the four recited resins. Multilayer Stretch, slip op at 21-22 (majority opinion). Drawing a distinction with the use of “consisting of” discussed in the first question, the Federal Circuit noted that the use of the transitional phrase “consisting of,” by itself, does not necessarily suggest that a Markush group is closed to mixtures, combinations, or blends. Id. at 22. Nonetheless, there is a presumption that a Markush group is closed to mixtures of the listed elements. Id. (citing Abbott, 334 F.3d at 1281). If a patentee desires mixtures or combinations of the members of the Markush group, the patentee would need to add qualifying language while drafting the claim. Id. Here, there is no express language in element (b) permitting “mixtures,” “combinations,” or “blends” of the four recited resins; thus, under Abbott, the Markush group of element (b) is therefore presumed closed to blends. Id. at 22-23. The question is whether that presumption can be overcome by a combination of other claim language and the specification itself. Id. at 23.

On this point, the Federal Circuit found that Multilayer had rebutted the presumption of excluding blends of the resins. The intrinsic evidence of the patent, in the claims and the specification, is unequivocal that the inner layers described in element (b) are open, not closed, to blends of the recited resins. Id.The claims themselves recite a metallocene-catalyzed linear low density polyethylene (mLLDPE), which is itself a subtype of LLDPE with a particular kind of catalyst. Id. at 24. Similarly, the specification supports construing element (b) as open to blends, as it repeatedly and consistently references blends in describing any and all resins, including the four resins of element (b). Id. Similarly, the specification “repeatedly and consistently references blends in describing any and all resins, including the four resins of element (b),” and discusses blending the resins in order “to achieve a desired range of physical or mechanical properties.” Id. at 25 (citation omitted). Finding “nothing in the prosecution history to suggest that blends are excluded,” the Federal Circuit found “this strong intrinsic evidence” requires “the Markush group be read as open to blends of the four listed resins.” Id.

While Markush claims can give the patent applicant some freedom to ensure full coverage of the scope of the invention, this does not negate the right of the public to know the boundaries of the claim. This Federal Circuit decision provides some useful pointers on how to do so. First, carefully choose the “generic” group for which the Markush group is offering alternatives. As noted by Judge Taranto, Markush group language typically recites “an X [being] selected from a group consisting of A, B, and C,” where A, B, and C are actually instances of X. Taranto Dissent at 3 (alteration in original). That is, the term X is a genus or generic descriptor. Id. In this case, instead of “each layer being selected from the group consisting of,” the claim could have been more clear and recite “each layer being made of a resin selected from the group consisting of.” Second, if mixtures or blends are within the scope of the claim, be sure to say so. As noted by the court, the presumption is that the Markush group is closed to blends and mixtures. Lastly, avoid being the applicant that “sometimes mistakenly write[s] dependent claims that invalidly add elements inconsistent with their independent claims.” Id. at 7. Be mindful to draft your dependent claims, ensuring that they are narrower than the precedent claims, and confirm that this remains consistent, even if the scope of the independent claims is narrowed during prosecution.