blanks serving for the production of insulating material and folding packs have to be provided with folding and bending lines . these folding and bending lines in the plastic foam must not break when the blank is folded . this is achieved according to the invention by embossing the folding and bending lines for forming the blank into the &# 34 ; fresh &# 34 ; web of material which for the most part still contains expanding agent . the folding and bending lines formed in this way have surprisingly proved to form durable hinge lines in the plastic foam material and make it possible to fold up the blank for forming a folding carton without it breaking or cracking .