PURPOSE: To produce a polyolefinic resin foam foamed in a high foaming ratios and perfectly prevented in the dimensional change with time without deteriorating the stability of the foam.

CONSTITUTION: A polyolefinic resin is mixed with a foaming agent and subsequently foamed. A foaming agent comprising 50-90wt.% of HFC-134a and 10-50wt.% of HFC-152a, a foaming agent comprising 30-65wt.% of HCFC-142b, 20-60wt.% of HCFC-124 and 5-30wt.% of HFC-152a, a foaming agent comprising 40-80wt.% of HCFC-124, 10-50wt.% of HFC-134a and 10-40wt.% of HFC-32, or a foaming agent comprising 40-80wt.% of HCFC-124, 10-50wt.% of HFC-A34a, and 10-40wt.% of HFC-152a is used as the foaming agent.