Abstract: The invention provides a process for the production of a 5 crosslinked polymer foam, which comprises the following steps: (I) blending a polymer with a blowing agent, (II) forming the blend into a sheet, (III) crosslinking the sheet, and (IV) foaming the sheet, wherein the blowing agent is blended in an amount of 3 to 25 based on the total weight of the polyolefin and the blowing agent, and is composed of (A) 3 to 50% of one or more inorganic carbonates and (B) 50 to 97 of one or more compounds selected from the group consisting of polycarboxylic acids, salts thereof, and derivatives thereof.