N.D. Illinois Upholds “Qualitative” Patent Claims Against Indefiniteness Challenge

The Northern District of Illinois granted a summary judgment motion of no invalidity based on indefiniteness because the qualitative terms like “sufficiently slow” and “desired period of time” were definite when viewed in light of the surrounding claim language and specification.
The patents at issue are directed to devices and methods for securing patients on tilted surgical tables using a foam pad to prevent slippage. Like memory foam, the foam pad is designed to deform to accommodate the patient’s weight and recover its shape slowly enough to keep an impression for some time, thus holding the patient in place. The claims of the patents include functional limitations that cover these characteristics of the pad material, including its ability to hold a patient in a “desired position” and the rate at which it is able to recover its shape.
Defendant challenged the validity of three such functional limitations--1) “rate of recovery sufficiently slow to maintain a depression in said pad for a desired period of time”; 2) “substantial portion of the holding forces”; and 3) “generally in a desired position.”—as indefinite under § 112. Plaintiff moved for summary judgment on Defendant’s affirmative defense of indefiniteness. 
Before reaching the merits of the motion, the district court noted that it previously granted Plaintiff’s Daubert motion and excluded Defendant’s expert testimony relating to indefiniteness. As the court explained, the expert erred by applying an “overly stringent” standard of mathematical exactitude, by attempting to import specific numerical thresholds into the claims that were not supported by the specification, and by “conflat[ing] indefiniteness with dissatisfaction about breadth” of the claims.  Without this testimony, “Surgitech effectively lack[ed] any expert evidence to support an assertion that these terms would confuse a person of ordinary skill in the art.”
The court then addressed the merits of the motion based on the remaining admissible evidence. The court’s most detailed analysis focused on the phrase “rate of recovery sufficiently slow…for a desired period of time,” where the court identified three layers of intrinsic support to find the phrase sufficiently definite.  First, the claim language itself tied “desired period of time” to a specific event—a change in depression-generating force on the pad—anchoring the phrase to an objective identifiable moment rather than a surgeon’s subjective preference.  Second, the specification expressly defined “rate of recovery” as the time for the foam to return to its starting shape—giving the term an objective, time-based meaning—and provided quantified example recovery time bands (e.g., 50-80% recovery in 2-10 seconds; full recovery in 10-35 seconds). Third, the specification described the functional role of the depression—holding the patient in place—as providing “desired period” with a clinically meaningful, operationally testable reference point. Based on this intrinsic record, the court found the patents provide sufficient context for a person of ordinary skill to determine whether a foam meets the claim limitation. In so doing, the court expressly rejected efforts by the Defendant to impose numerical limits on the claims.
The court applied similar reasoning to the other two challenged terms. For “substantial portion of the holding forces,” the court noted that the specification explains that the depression provides “primary holding” for the patient on the tilted table, with body straps described as optional. This disclosure thus provided a boundary between a trivial and a significant holding contribution. Defendant argued the specification provided no way to measure or quantify the “holding forces” sufficient to meet the claim. Its expert, however, conceded that a person of ordinary skill could determine whether “a substantial portion” of the holding force came from the pad by a simple functional test: tilt the table without straps and observe whether the patient slides. That concession reinforced that the term is testable, and not merely subjective. For “generally in a desired position,” Defendant argued the phrase required a specific “coefficient of static friction” that the patents failed to define. The court rejected that argument because “coefficient of static friction” appears only in dependent claims, and under the doctrine of claim differentiation, importing it into the independent claim would improperly read a limitation into claims that the patentee did not include there.
Practice Tip: Patent drafters have freedom to use qualitative descriptors in their claim terms and need not include numerical cutoffs. However, when using qualitative terms, drafters should take care to ensure that the claim language and specification anchor the terms in objective criteria, such as by providing functional context, express definitions, and quantified examples. In other words, the specification should include some sort of reference point or method that can be used to consistently assess whether the functional limitation is met. Absent this support, a functional limitation may be susceptible to an indefiniteness challenge.
Xodus Med., Inc. v. U.S. Surgitech, Inc., No. 1:19-cv-03164 (N.D. Ill. Jan. 30, 2026).