A composite extrusion, such as a fiber, film or ribbon, having an inner core and an outer sheath, wherein the inner core is made of a molecularly oriented polymer capable of being rigidified by imposition of a temperature gradient and the sheath is made of a polymer wherein its molecules are generally not oriented. A method of making such a composite extrusion utilizing melt transformation coextrusion wherein the inner core-forming material is caused to assume a molecular orientation coaxial to the longitudinal axis of said core while in a molten state and then forced through a reducing die while being subjected to a temperature gradient while surrounded by the liquid sheath-forming material such that crystallization in at least the outer skin of said core occurs within the die but the sheath-forming material does not crystallize until the extrudate exits the die.