A delivery sheath includes an outer tubular layer and an initially folded inner tubular layer. When an implant passes therethrough, the outer tubular layer expands and the inner tubular layer unfolds into an expanded lumen diameter. The sheath may also include selectively placed longitudinal support rods that mediate friction between the inner and outer tubular layers to facilitate easy expansion, thereby reducing the push force needed to advance the implant through the sheath's lumen.