Abstract: A crushing part or component of a gyratory grinder or other crushing, grinding or material-reducing machine is provided with a shock-absorbing backing material which has improved toughness and resilience and is formed of a filled polyurethane resin composition the resin component of which is derived from a cold-curing system comprisingI. at least one polyether polyol having more than 2--OH groups per molecule,Ii. at least one polyol containing both ester and ether groups and having more than 2--OH groups per molecule,Iii. at least one polyether diol andIv. at least one aromatic polyisocyanate, there being an excess of CNO groups over --OH groups in the system.