Patent ID: 7300704

Claim:
A multilayer film for roofing membranes having at least two film layers made from different materials; wherein the film layers have different coefficients of thermal expansion; wherein said at least two film layers comprise a first film layer made from a polyolefin and a second film layer made from a polyolefin or a polyacrylonitrile, said second film layer having a larger coefficient of thermal expansion than said first film layer, whereby the first film layer is adapted to be closer to a substrate to be covered with the multilayer film than the second film layer; wherein at least the first film layer of the multilayer film is a barrier against mineral oils; wherein at least one surface of the multilayer film is treated so that it has low bonding properties; and wherein a second barrier layer against oils, oxygen or UV radiation of lacquer is provided between said first film layer and said second film layer; and wherein one side of the first film layer is coated with a silicone layer.