The present invention is for method and means by the manufacture of a product of expanded polymer, by which is obtained a weight per unit volume which is essentially lower than that of homogeneous expanded material. The starting material according to the invention can be either a specifically manufactured starting material or scrap and recovered material. The pieces of expanded polymer are supplied in controlled quantities through a feeder to a space for the application of glue drops which are sprayed into the space from one or more dies. In the space the pieces of polymer are dried by means of micro-wave energy which is obtained from an energy generator and magnetrones. The dried pieces then are discarded from the space together with the air flow through the opening. By the manufacture of a product according to the invention one starts from the pieces with glue applied to them as described above. The pieces are put into a mould wherein they are pressed against each other. Thereupon the material is heated so that the glue becomes sticky and the pieces attach to each other. The heating is done by means of microwave energy which finds its way into and homogeneously heats the whole volume of material.