The present invention relates to a method for manufacturing a composite element comprising a single- or multi-part core and an envelope which are in a force fit combination with each other, at least comprising providing a single- or multi-part core of an evacuable organic material; at least partly enveloping the core with an envelope to obtain a composite element precursor; and treating the composite element precursor for a period leading to an at least partial softening of the evacuable organic material and of the envelope surface apposing the core. The present invention further relates to composite elements obtained or obtainable by a method of the present invention and also to the method of using a composite element of the present invention as a vacuum insulation panel or as a thermal insulation material.