To attain excellent flexibility and mechanical characteristics, compression set in particular, at a high temperature by allowing an elastomer to comprise a block copolymer of a polyester-based copolymer with a polyether linked together by an isocyanate and have a specific storage elastic modulus.

There is provided an elastomer comprising a block copolymer of a polyester-based copolymer composed of 50-95 wt.% of a short chain component of formula I and 50-5 wt.% of a long chain component of formula II with a polyether composed of formula III linked together by an isocyanate component of formula IV or V and having a storage elastic modulus (23°C) of 4×107-4×108 Pa. In the formulae, R0 is a 6-12C hydrocarbon; R1 and R3 are each a 2-8C alkylene; R2 is -R-O having a number average mol.wt. of 500-5,000 (wherein R is a 2-8C alkylene); and R4 is a 2-15C alkylene, phenylene or a combination of methylene with phenylene.