Abstract: A net formed integrally of blended incompatible polymers, with parallel smooth longitudinal ribs interconnected by a plurality of split strands non-uniformly interspersed with a plurality of differently sized voids, by stretching a film with a generally longitudinal set of parallel primary grooves and a transverse or angled set, on the other surface, of parallel secondary grooves.

Abstract: A melt-embossed polymer film with primary parallel grooves on one surface and secondary parallel grooves on the other surface such that the combined tapes of the grooves is at least substantially equal to the film thickness, the two sets of grooves being located at an angle to each other of not less than 30.degree., is stretched at right angles to the direction of the primary grooves by a small amount to give a perforate product which can be formed into strips tearable longitudinally or transversely and thus useful as a vapor-permeable substrate for adhesive-coated tape.