A method for producing a heat-shrinkable product is provided. First, a polymer composition containing a polymer, a crosslinking agent and a micro-encapsulated foaming agent uniformly dispensed therein is melt mixed. The foaming agent has a peak activation temperature which is higher than a temperature of the melt mixing. Next, the polymer composition is injection molded into a molded product. This carried out at the peak activation temperature to activate the foaming agent. Then, the molded product is crosslinked within the mold.

A physically crosslinked foamable particle comprises a polyolefin resin and a chemical foaming agent, the foamable particle having a volume of at least about 0.002 mm.sup.3.