Although poly(vinyl alcohol) is amorphous when unstreched, it can be drawn into a crystalline fiber, the hydroxyl groups being small enough to fit into a crystal lattice despite the atactic chain struture. Poly(vinyl alcohol) does not melt to a thermoplastic, but decompoese by loss of water from two adjacent hydroxyl groups at themperatures above 150. Double bonds are left in the chain, and, as more of these are formed in conjugate positions, severe discoloration take place.