An embossed thermoplastic film characterized in that one surface of the film is provided with a plurality of rows of protuberances having the shape of pyramids with square bases which extend perpendicular to both the longitudinal and the transverse axes of the film. The protuberances are joined at the...http://www.google.de/patents/US4343848?utm_source=gb-gplus-sharePatent US4343848 - Embossed thermoplastic material
