Abstract: Process for the preparation of bodies of expanded cross-linked polyethylene, with closed cells, comprising the steps of:melting a polymer of ethylene selected among ethylene homopolymers, copolymers of ethylene with alpha-olefins, copolymers of ethylene with conjugated diolefins and relevant mixtures;homogenizing the polymer of ethylene in the molten state with a quantity of from 0.1 to 2.5% by weight of a cross-linking agent and with a quantity of from 2 to 25% by weight of an expanding agent, the cross-linking agent and expanding agent having a decomposition temperature higher than the melting point of the polymer of ethylene, the homogenizing step operating at temperatures of from 130.degree. to 150.degree. C., and for times of from 5 to 10 minutes;forming the homogeneous mixture in a solid parallelepiped shape by means of extrusion and subsequent cooling, or by means of moulding wherein the extrusion or moulding step is operated at temperatures within the range of from 130.degree. to 150.degree. C.