 TPU is a block copolymer consisting of alternating sequences of hard and soft segments or domains formed by the reaction of (1) diisocyanates with short-chain diols (so-called chain extenders) and (2) diisocyanates with long-chain diols.By varying the ratio, structure and/or molecular weight of the reaction compounds, an enormous variety of different TPU can be produced.This allows urethane chemists to fine-tune the polymer's structure to the desired final properties of the material.