Abstract: An electroconductive cross-linked polyolefin foam having electric resistance of not more than 100 M.OMEGA. and comprising uniform minute cells and proving useful for the production of IC cases, etc. is provided by a method which comprises kneading 100 parts by weight of a polyolefin, 10 to 30 parts by weight of carbon particles, and suitable amounts of a foaming agent and a cross-linking agent and heating the resultant cross-linkable and foamable composition under atmospheric pressure thereby allowing the composition to be cross-linked and foamed without being abruptly foamed or expanded or by a method which comprises heating the aforementioned cross-linkable and foamable composition in a metal mold under pressure to a temperature at which the foaming agent is not substantially decomposed thereby cross-linking the composition and then heating the resultant cross-linked foamable composition under atmospheric pressure thereby allowing the composition to be foamed without being abruptly foamed or expanded.

Abstract: An open-cell foamed article of a cross-linked polyolefin having a high open-cell ratio and a high degree of expansion is produced by a method which comprises the steps of preparing a foamable and cross-linkable polyolefin composition, forming the composition into a desired shape maintaining its gel percent at zero, decomposing the cross-linking agent and blowing agent concurrently by heating the composition under atmospheric pressure in such conditions that the peak of the ratio of the degree of cross-linking to the degree of decomposition of the blowing agent is not more than 20 and exerting a mechanical deformation to the resulting polyolefin foam to rupture the cell membranes.