PURPOSE: To obtain the subject foam with an optimized glass transition point by reacting a specific polyol mixture with a specific polyisocyanate in the presence of water as a blowing agent under specified conditions.

CONSTITUTION: This polyurethane foam is obtd. by reacting a polyol mixture having a specified OH value with a polymethylene polyphenylene polyisocyanate in the presence of a specified amt. of water as a blowing agent at a specified isocyanate index. The polyol mixture comprises a polyoxyalkylene polyol which has specified mean functionality, OH value, polyoxyethylene unit content, and primary OH content, a polyoxyalkylene polyol which has specified mean functionality and OH value and is obtd. by using a nonamine compd. as the initiator, and a polyoxyalkylene polyol which has specified mean functionality, OH value, and primary OH content and is obtd. by using a nonamine compd. as the initiator each in the specified value of the isocyanate index.