In this process, the shoe manufacturer does not use pre-prepared raw materials, but two or more liquid components in the chemical reaction (gradual addition polymerization) produced by the raw materials. In short, the two liquids must be intensively mixed when they are made into raw materials, and then injected into a closed unit, waiting for the raw materials to react to form PU. Therefore, raw material A is either polyester or polyether (polyol), while raw material B is isocyanate. Polyester polyol systems are more resistant to mechanical wear, high temperature and chemical reactions than polyethers (polyhydroxy compounds), which is why polyester polyols are more suitable for use in the production of safety shoes.
