a process for embossing flexible polymeric substrates in a dielectric heating press having a platen and a design fixture by placing an insulating blanket of a composite sheet structure between the substrate being embossed and the platen of the press and embossing the substrate ; wherein the composite sheet structure is an aromatic polyamide fabric coated on both sides with a 2 - 30 mil thick layer of a fluorosilicone rubber and having a dielectric constant of about 4 - 8 and a dissipation factor of about 0 . 015 - 0 . 030 ; the polymeric substrates generally are laminates of thermoplastic polyurethane form / short napped synthetic velour fabric used as upholstery for automobiles and trucks .