In Multilayer Stretch Cling Film v. Berry Plastics, the Federal Circuit provided a detailed discussion of the construction of claims that use Markush group language. The decision emphasizes the closed nature of the “consisting of” terminology, and underscores the care that should be used with Markush group claim language.

The Markush Group Language At Issue

The patent at issue was Multilayer’s U.S. Patent No. 6,265,055, directed to what the court referred to as “multilayered plastic cling wrap films.” Claim 1 is representative:

  1. A multi-layer, thermoplastic stretch wrap film containing seven separately identifiable polymeric layers, comprising:
  1. two identifiable outer layers, at least one of which having a cling performance of at least 100 grams/inch, said outer layer being selected from the group consisting of linear low density polyethylene, very low density polyethylene, and ultra low density polyethylene resins, said resins being homopolymers, copolymers, or terpolymers, of ethylene and alpha-olefins; and
  2. five identifiable inner layers, with each layer being selected from the group consisting of linear low density polyethylene, very low density polyethylene, ultra low density polyethylene, and metallocene-catalyzed linear low density polyethylene resins; said resins are homopolymers, copolymers, or terpolymers, of ethylene and C3 to C20 alpha-olefins; wherein each of said two outer layers and each of said five inner layers have different compositional properties when compared to a neighboring layer.

Construction of clause (b) of claim 1 and similar language in claim 28 was in dispute. The district court construed the clause as requiring that “each of five identifiable inner layers must contain only one class of the following resins, and no other resin(s): linear low density polyethylene [(LLDPE)] resins, very low density polyethylene [(VLDPE)] resins, ultra low density polyethylene [(ULDPE)] resins, or metallocenecatalyzed linear low density polyethylene [(mLLDPE)] resins.”

Marksuh Group Claim Language

As explained in the Federal Circuit decision, “[a] Marksuh group lists specified alternatives in a patent claim, typically in the form: a member selected from the group consisting of A, B, and C,” where “[i]t is generally understood that . . . the members of the Markush group . . . are alternatively usable for the purposes of the invention” (internal quotations and citations omitted). The clause at issue is “a Markush group that lists four species or types of resin—LLDPE, VLDPE, ULDPE, and mLLDPE—which are understood to be alternately useable for preparing the inner layers of the claimed film.”

The Federal Circuit Decision

The Federal Circuit decision was authored by Judge Dyk and joined by Judge Plager. Judge Taranto dissented in part. The Federal Circuit identified two claim construction issues surrounding the Markush language:

  1. whether the Markush group of element (b) is closed to resins other than the listed four
  2. whether the Markush group is closed to blends of the four listed resins

The Federal Circuit determined that the Markush language is closed in first respect, but not the second. Judge Taranto dissented as to the majority’s determination on the first issue.

In reaching its decision on the first issue, the Federal Circuit emphasized the “closed” nature of the “consisting of” phrase as compared to the “open-ended” term “comprising”:

Use of the transitional phrase “consisting of” to set off a patent claim element creates a very strong presumption that that claim element is “closed” and therefore “exclude[s] any elements, steps, or ingredients not specified in the claim.” …. By contrast, the alternative transitional term “‘comprising’ creates a presumption that the recited elements are only a part of the device, that the claim does not exclude additional, unrecited elements.”

The Federal Circuit reached this claim construction even though the specification described inner layers having an unlisted resin (LDPE), and even though several dependent claims recited inner layers that comprise LDPE. On this point, the court stated:

[T]he language of a dependent claim cannot change the scope of an independent claim whose meaning is clear on its face. …. “The dependent claim tail cannot wag the independent claim dog.”

Thus, the dependent claims that do fall within the scope of claim 1 as construed by the Federal Circuit are invalid.

In contrast to its analysis on the first issue, the Federal Circuit was swayed by the intrinsic record on the second issue. The court first referred to its decision in Abbott Labs. v. Baxter Pharm. Prods., Inc., 334 F.3d 1274 (Fed. Cir. 2003):

Abbott held that if a Markush claim recites “a member selected from the group consisting of A, B, and C,” the claim is presumed to permit the member to be one and only one of A, B, or C, and to exclude mixtures or combinations of A, B, and C.

However, the Federal Circuit also noted the “presumption can be overcome by a combination of other claim language and the specification itself.” Indeed, the court emphasized the overarching principle of claim construction:

All patent claims, including Markush claims, must be construed in view of “the words of the claims, the specification, the prosecution history, and any relevant extrinsic evidence.”

The Federal Circuit found that in this case, “the intrinsic evidence of the ’055 patent is unequivocal that the inner layers described in element (b) of claims 1 and 28 are open, not closed, to blends of the recited resins.” For example, the court noted that 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.” 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.”

Choosing Your Claim Language Carefully

This decision is an important reminder of the care that should be taken with all claim language, and indicates that extra caution may be warranted whenever any “consisting of” clause is used. It is not clear whether Multilayer could have modified the Markush clause with open-ended language, such as by reciting that “the inner layers comprise a resin selected from the group consisting of ….” Some examiners raise indefiniteness rejections when a claim uses both “comprising” and “consisting of ” language, but not all combinations of such “open” and “closed” language are improper.