A high quality material which shrinks to 1/2 its size.  Polyolefin is stable, and can be stored for extended periods of time without shrinkage.  It remains flame retardant, and is very flexible.  Available in the following diameters:  1/8", 1/4", 3/8", 1/2", 3/4", 1", 1 1/2" and 2".  Pieces are 4 feet in length.