A single screw extrusion process for extruding a mixture of relatively high molecular weight thermoplastic elastomer particles and relatively low molecular weight resin particles, wherein the particulate mixture is supercooled and maintained at temperatures below that which would cause the mixture to agglomerate and stick to the screw until the axial driving forces on the mixture have increased to the extent they will overcome any tendency of the mixture to stick to the screw, thereby assuring steady state extrusion conditions.