PPG Industries v. Guardian Industries Corp., No. 97-1513, 1998 U.S. App. LEXIS 24577 (Fed. Cir. Oct. 1, 1998).


A claimed invention does not "consist essentially of" an unlisted ingredient that has a "material effect" on the basic and novel properties of the invention as a factual matter.



PPG holds U.S. Patent No. 5,240,886 (the '886 patent), directed to a green-tinted "solar control glass" that contains "a colorant portion consisting essentially of CeO2 less than 0.5 weight %, total iron greater than 0.85 weight % (as Fe2O3), [and] FeO/total iron less than 0.275 . . ." with specific light transmittance characteristics. The parties agreed that color, composition, and light transmittance are the three basic and novel characteristics of the glass.  One improvement of this invention is that, through the use of high levels of ferrous (Fe2+) and ferric (Fe3+) iron at a low redox ratio (ferrous to total iron), only a minimal amount of cerium oxide (CeO2) is needed to provide the desired reduction of light transmittance.  This reduces the cost and increases the ease of glass production.

PPG preferably produces the glass of this invention by the float method, whereby the glass is cooled in sheets on a pool of molten tin.  To reduce bubbles in the finished product, "melting and fining aids such as SO3" may be added. PPG Indus. at para. 21.  Such compounds predominantly dissipate during the cooling process; some sulfate, however, remains dissolved in the finished glass.  Though generally this has no effect on the color of the glass, strongly oxidized conditions are produced at the interface with the molten tin which causes the formation of sulfide ions (S2-).  These ions combine with ferrous iron to produce iron sulfide (FeSx), which is yellowish-brown and results in a 0.5% change in the total light transmittance of the glass, as well as a 3 nanometer shift in its color (light transmittance).  Iron sulfide is not listed as an ingredient in the '886 patent.

PPG brought suit against Guardian alleging that Guardian's production of "Solar Management Glass" ("SMG") infringes the '886 patent.  SMG glass also is a green-tinted glass, produced by the float method, and contains high levels of iron oxide as a colorant.  SMG glass contains no cerium oxide.  At trial, the district judge instructed the jury that a product "consisting essentially of" certain specified ingredients may also contain unlisted ingredients that "do not have a material effect on the basic and novel characteristics of the glass [color, composition, and light transmittance]." PPG at para. 14.  Whether the amount and presence of iron sulfide in the glass was material was left to the jury as a factual matter; no definition was provided by the judge of exactly what changes would be material in this context.  The jury concluded that SMG glass was outside of the scope of the '886 patent, and therefore did not infringe.



1. Whether the district court erred in treating as a factual issue the question of whether iron sulfide introduced by the float process had a material effect on the invention, rather than treating it as a matter of claim construction for the judge to determine.

2. Whether the district court erred in not providing the jury with what constituted a material change in the basic and novel characteristics of the invention.

3. Whether the district court erred in denying PPG's motion to overturn the verdict on the ground that no reasonable jury could have found that introduction of iron sulfide by the float process was a material change with respect to the glass so produced.


1. No. The patent claim language "consisting essentially of" is inherently ambiguous and must be dealt with as such by the finder of fact; the court may not give a claim more precision or specificity than was provided by the language of the patent itself.

2. No. Where the specification provides no clear definition, and the definition urged by PPG at trial is both contrary to the understanding of one of skill in the art and would allow for the addition of sufficient sulfur compound to effectively change "consisting essentially of" to "comprising" in the claim, the court is not required to provide such a definition.

3. No. There was sufficient evidence submitted at trial for a reasonable jury to find both that the amount of iron sulfide introduced was material, and that the amount present in SMG glass was significantly higher than that found in PPG's glass such that the two types of glass were not identical.


Cases Cited by the Court

Other Sources Cited by the Court


State of the Law Before PPG Industries

The applicant for a patent may provide its own definition for terms used in its patent claim, including the transition phrase, "consisting essentially of" to signal that the claim is partially open.  This means that the claim sets out a list of ingredients in a composition claim that materially affect the product or process.  The claim is considered to be partially open because the product or process may include unlisted ingredients that do not materially affect the basic and novel properties of the invention.  Such immaterial ingredients should not be considered by the trier of fact as distinguishing the accused invention from the patented one.

The phrase "consisting essentially of" falls between two other levels of inclusion of non-material ingredients--"consisting of" and "comprising."  The former is the most exclusive transition phrase, indicating that the invention only includes those ingredients specifically enumerated in the claim. See Ex Parte Davis, 80 U.S.P.Q. 448, 449-50 (1948).  "Comprising" is the most inclusive of non-material ingredients. Id.  The phrase "consisting essentially of" breaks down into two conflicting elements.  "Consisting" has been interpreted by the courts as "definitely excluding therefrom any element or ingredient not specified therein." Id.  For the word "essentially" to have meaning, however, the phrase as a whole must be read to permit other elements that are not necessary or material to the invention. See Markman v. Westview Instruments, Inc., 52 F.3d 967, 34 U.S.P.Q.2d (BNA) 1321 (Fed. Cir. 1995), aff'd, 517 U.S. 370, 38 U.S.P.Q.2d (BNA) 1461 (1996).

There is no question that claim construction is within the province of the court.  Judges are allowed to give a claim whatever additional precision or specificity is "warranted by the language of the claim." PPG Indus. at para. 17.  This does not mean that judges can give a claim whatever additional precision is necessary to facilitate a comparison between the claim and the accused product. See id.  The trier of fact is responsible for whether the accused product infringes. See Modine Mfg. Co. v. U.S. Int'l Trade Comm'n, 75 F.3d 1545 (Fed. Cir. 1996).

Effect of PPG Industries on Current Law

The patent practitioner must now be aware of the consequences of using the transition phrase "consisting essentially of" in claim construction.  First, the practitioner must be aware of how the court views claim construction when this transition phrase is used.  Second, the specification must be extremely clear in identifying those unlisted ingredients that do have a material effect on the basic and novel properties of the invention.  When an unlisted ingredient does not have a material effect on the basic and novel properties of the invention, it will be deemed to fall within the claim limitations.

Inherent Imprecision

The court stated that there is some "inherent imprecision" that results from using the phrase "consisting essentially of." PPG Indus. at para. 19.  This imprecision leaves a patent that uses "consisting essentially of" language open to various interpretations by the fact finder which, as in this case, can lead to an unfavorable result in an attempt to enforce a patent in court.  While the Court agreed with the appellant that claim construction is a question of law for a judge to decide, it stated that when a claim is ambiguous, a court may not "under the rubric of claim construction . . . give a claim whatever additional precision or specificity is necessary to facilitate a comparison between the claim and the accused product." PPG Indus. at para. 17.  After the court interprets the claims, the finder of fact decides whether the accused device falls within the scope of the claims.

In this case, the court held that the trial judge properly construed the claims and correctly gave the jury the task of determining whether iron sulfide had a material effect on the basic and novel characteristics of PPG's invention.  PPG did not mention iron sulfide specifically in the patent specification and consequently the court refused to interpret language in the specification to encompass all sulfur compounds as PPG desired.  Thus, as a result of this lack of clarity, and the "inherent imprecision" resulting from use of the phrase "consisting essentially of," the question of what constituted a material effect went to the jury.

Precision is Required in the Specification

The patent practitioner is advised to be extremely precise in the patent specification regarding unlisted ingredients that have a material effect on the invention and those that do not when using "consisting essentially of" language.  The Court stated that PPG could have defined the scope of its claim by "making clear in its specification what it regarded as constituting a material change in the basic and novel characteristics of the invention." PPG Indus. at para. 21.

Precision is especially essential if an unlisted ingredient has a material effect in some amounts but not in others.  Those amounts where there is no material effect, in which case the ingredient would come within the claim limitations, must be identified as such in the specification.  In this case, the PPG specification did state that residual amounts of sulfate could vary and have no material effect on properties of the invention.  Expert testimony was introduced which indicated that iron sulfide, however, would change the properties of the invention significantly.  Again, PPG did not mention iron sulfide specifically in the specification, which proved costly.

While it is true that iron sulfide in various amounts could alter the properties of the invention significantly, the amount used by Guardian resulted in a change in the dominant wavelength by 3 nanometers and altered the ultraviolet and visible light transmittance by 0.5%.  This does not appear to be a significant change, but the question went to the jury and the jury found otherwise.  Had PPG precisely stated in the specification the amounts of iron sulfide that would only cause non material changes in the novel and basic properties of the invention, the court seems to indicate that there would have been no question of materiality for the jury to decide.  The patent would have been infringed.

Thus, as a result of this holding, when using the transition phrase "consisting essentially of," the utmost clarity, precision, and specificity must be demonstrated to avoid a result such as this.

Unanswered Questions

Would the usage of the term "consisting essentially of" in claim language be able to survive in the future under the impact of this case?

Does the court's decision to let the jury determine what constitutes a material effect on properties of a claimed invention undermine the holding of the Markman decision?

Would the court have decided the case differently had it based its decision on the doctrine of equivalents?

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