Polyurethane (PMC-860)

This toffee-coloured opaque polymer is an industrial-strength urethane rubber. You can buy this in a liquid form and it can cast with it without the need for specialist machinery. It can be used in demanding applications as it is extremely tough and moulds made from this material can be reused again and again for casting materials as hard as concrete. Regardless of the end-product or even type of polyurethane you are using, the way in which you use polyurethane resins is always the same: the raw materials come in two parts, a liquid isocyanate (a very reactive chemical derived from petroleum) and a polyol (a long-chain alcohol), which are mixed to a specified ratio to create a reacting liquid, which is then poured into a mould or onto a surface and left until it cures to form a solid object. This relatively low-tech process makes it a useful material for the making prototypes.