Film structure of at least five layers, two outer layers (2) made of a polyolefin on which is each time provided, on the opposite sides, a layer (4) forming a gas barrier and whereby, between both above-mentioned gas barriers (4), is provided a layer (3) made of a foamed synthetic material, whereby the outer layers (2) consist of a mixture of a polyolefin and a binder, which makes it possible to bond this polyolefin with the layer (4) forming the gas barrier.