Estoppel is a word rarely used by the layman. It is a hothouse flower that seems able to grow only in the rarefied loam of the law, dying quickly when exposed to modern vernacular. \
But it was not always so. Like much legal jargon, it springs from old French, and in particular "estopail" which meant the plug you put in a barrels bunghole to prevent your wine from leaking out.
But I digress.
Today's opinion in Cognipower LLC v. Fantasia Trading LLC, C.A. No. 19-2293-JLH-SRF (D. Del.) dealt with a rather novel estoppel argument I hadn't seen before. The Defendant had filed multiple IPRs on the many asserted claims at issue. The PTAB had issued a final written decision on the IPR covering the independent claims, but did not institute the petitions covering the dependent claims. Plaintiff filed an SJ motion seeking to estop the defendant from using the prior art from the independent claim IPR to invalidate the dependent claims.
Judge Hall denied that motion and found that estoppel did not apply in a short order which noted that "IPR estoppel applies only to those claims 'included in the petition' where the petition results in a final written decision . . . [and] the dependent claims that Anker contends are invalid over the Mammano et al. combination were not included in any petition that resulted in an instituted IPR for which the Patent Trial and Appeal Board issued a final written decision." Cognipower LLC v. Fantasia Trading LLC, C.A. No. 19-2293-JLH-SRF, D.I. 401 (D. Del. Aug. 5, 2025)
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