There is described an isocyanate-based polymer foam having a V-0 rating according to Underwriters' Laboratories Standard 94 Flammability Test after aging of separate samples of the foam (i) for 168 hours at 150 C., and (ii) for 600 hours at 120 C. The foam may be in the form of a molded foam or a slabstock foam. The foam may be used in vehicular applications, such as an under hood application.