A polyisocyanate-based elastomer having a ratio of the storage modulus (E') at 20.degree. C. and the storage modulus (E') at 120.degree. C. of between 0.75 and 1.5, a tan .delta. at 100.degree. C. of less than 0.1 and a maximum value of the tan .delta. of more than 0.8, the tan .delta. being the ratio of the loss modulus (E'') and the storage modulus (E').