PURPOSE: To obtain a polyurethane which is excellent in moldability and the resistances to heat, cold, and hydrolysis and has a low compression set by reacting a specific polyester diol, an org. diisocyanate, 1,4-butanedioi, and an aliph. diol.

CONSTITUTION: A polyurethane is produced by reacting a polyester diol represented by formula I, an org. diisocyanate, 1, 4-butanediol, and an aliph. diol represented by formula II. In the formulas, m is 5-10; a is the number of moles of the polyester diol; b is that of the diisocyanate; c is that of 1,4- butanediol; and d is that of the aliph. diol. Examples of a favorable aliph. diol are 1,6-hexanediol and 1,9-nonanediol, the latter being more favorable.