changing durometer of polyurethane

As opposed to PVC, where different durometers are achieved by varying the plasticizer content, in the case of TPU different durometers are realized by using different amounts and types of the base monomers (Polyol + Isocyanate) in the synthesis of the material. This approach is called "internal plastification". There is a trick, though, used by TPU-manufacturers (Bayer, Dow etc) to vary the durometer of a given TPU-formulation within a certain small range. The trick is to compound certain "white oils" into the material. If this is not done properly, the oils will "sweat out" with time leading to sticky surfaces and possibly surface cracks. I strongly recommend you not to try this yourself, because you will very likely run into this type of problem. I suggest you talk to your supplier and purchase a TPU-grade with the durometer you need.

Polyurethane is made from polymerization of isocyantes and polyools.

Changing the polyol and/or changing the isocyante composition will change the hardness.

Depending on your jacket reuirement and how much decrease in hardness you desire, there are three variables to manuveur: polyol(s), isocyantes, processing temperature.