PURPOSE: To provide the titled composition capable of giving highly heat- and solvent-resistant expanded surface free from stickiness and yielding phenomena, comprising terminal isocyanate group-blocked urethane prepolymer, polyamine- based corsslinking agent, heat-decomposable foaming agent and solvent.

CONSTITUTION: The objective composition can be obtained by incorporating (A) a solution of blocked urethane prepolymer which is prepared from (i) a polyol with a molecular weight 400W4,000 and (ii) polyisocyanate followed by blocking the resultant terminal isocyanate group by e.g. methylethyl hetone oxime with (B) a crosslinking agent such as iminobispropylamine, (C) heat-decomposable foaming agent such as diazobenzene with its decomposition point similar to the dissociation temperature of the component (A), pref. the difference between them being smaller than 20°C, and, optionally, (D) foam stabilizer, pref. filler, etc. Said composition is coated on a base, being expanded while distilling off the solvent contained to form a crosslinked expanded layer. The amount of said foaming agent to be used is 2W20(pref. 4W15)pts.wt. per 100pts.wt. of the polyurethane resin.