The invention relates to a method of in vitro testing of the efficacy of a potentially active substance comprising monitoring the effect of said potentially active substance on an artificial skin, comprising a composite product forming a collagen support comprising at least one porous collagen layer covered on at least one side with a collagen membrane component selected from the group consisting of a collagen membrane prepared by compression of a collagen sponge at a pressure of at least about 50 bar and of a collagen membrane comprising a collagen film prepared by drying a collagen gel separately from the porous collagen layer, thereby providing a reliable method for finding new potentially active substances.