Abstract: A method of producing a composite stratiform material uses at least one extruder having a pair of co-rotating screws to co-extrude at least three layers, each layer having polypropylene and at least one filler. In a carrier layer the filler is particulate organic filler, and in first and second outer layers the filler is an inorganic filler. The co-extrusion provides for interfusion of the carrier layer with the outer layers at mutually opposite layer interfaces. The particulate organic filler of the carrier layer is either vegetabilic or wood which is extruded by a co-rotational extruder. The inorganic filler is introduced into at least one second extruder for extruding at least one of the outer layers.

Abstract: A composite stratiform material (1) having at least three interfused layers and comprising:(I) a carried layer (10) formed of a mixture containing polypropylene and a particulate organic filler;(II) a first outer layer (12) interfused with said carrier layer at a first interface (11) and consisting essentially of a mixture containing polypropylene and an inorganic filler;and (III) a second outer layer (14) interfused with said carrier layer at a second interface (13) located opposite said first interface (11) and consisting essentially of a mixture containing polypropylene and an inorganic filler.