Disclosed is a method for continuous extrusion coating of a hollow core material with a highly expanded polyolefin resin, which is characterized by subjecting an extruded molten mass of an expandable polyolefin resin to external cooling at the point at which said molten mass begins to foam and supplying said hollow core material with the surface temperature thereof kept below the softening point of said polyolefin resin for thereby enhancing the fastness of adhesion of the highly expanded polyolefin foam with the hollow core material and at the same time facilitating the release of the two materials thus joined.