An article suitable for use as an insulating or coating material comprises a radiation-crosslinked composition comprising a polyethylene, a polypropylene and optionally an ethylene-propylene elastomer. The polyethylene component is selected from high density polyethylene (HDPE), medium density polyethylene (MDPE) and linear medium density polyethylene (LMDPE) and the polypropylene component is either a homopolymer or copolymer. The composition is predominantly based on the polyethylene component and contains the polyethylene component in an amount of at least 50 percent by weight. The article is radiation-crosslinked to a sufficient degree that it possesses thermoset properties, such that when the article is heated to a temperature above the crystalline melting point of the polypropylene homopolymer or copolymer, it is softened but does not become liquid. The article is formed by first blending the polyethylene, polypropylene and optionally the ethylene-propylene elastomer, melt processing the blend to produce an article, crosslinking the article by exposing it to radiation, and optionally heating, stretching and cooling the article to impart heat shrinkability to the article.