Polypropylene

This is the lowest density common plastic.  It floats easily, can be sterilized by boiling, has a high luster surface, molds easily and fast replacing other plastics in the electronics industry as a component material.  It will not absorb water, and it resists most chemicals and solvents.  It is flexible, but has poor wear resistance.  Hinges molded in polypropylene will frequently exceed one million flexing without failure.  Low cost.