Polyurethane-91 is a urethane polymer formed by a multi-step process. First, a polyester is made by reacting Hexanediol with Dimethyl Carbonate. A mixture of this polyester, 3-dimethylamino-1,2-propanediol and 1,4-Butanediol is reacted with Isophorone Diisocyanate. The polymer is neutralized with Lactic Acid.