Abstract: A foamable organic composition comprising a compound foamable to 50% or more comprising an organic polymer and a chemical foaming agent, and, as a physical foaming agent, at least one member selected from the group consisting of rare gases and carbon dioxide; and a method for producing a foamed article having a high expansion ratio by using said composition. According to the present invention, a foamed article having a uniform and fine foam structure and a high expansion ratio of not less than 75% (which is as high as when freon gas is used) can be obtained without causing environmental problems such as depletion of the ozon layer. When applied, in particular, to a foamed layer for an insulated conductor, such as foam-insulated electric wire which is required to have high performance insulation and is occasionally installed under severe conditions, the composition of the present invention advantageously provides an insulated conductor with no potential buckling.

Abstract: Polymer compositions for molding in the presence of a foaming agent which comprise at least a polyolefin resin as a base resin and low polarity boron compound powder which is not decomposed at a foaming temperature, such as boron nitride powder as a nucleator. Polymer compositions of the invention are useful for formation of a foamed insulating layer on a conductive material by way of foam molding. By using said polymer composition, a foamed insulating layer excellent in insulation properties which has small dielectric loss factor, tan .delta., at high frequency and high extent of foaming of not less than 70% can be obtained.