This British Standard specifies compositional and physical property requirements for four non-black natural rubber compounds designated W40, W50, W60, W70, three non-black natural rubber/zinc oxide compounds designated Y40, Y50, Y60 and five black natural rubber compounds designated Z40, Z50, Z60, Z70, Z80.
These compounds are intended for the manufacture of items in the form of mouldings, moulded or calendered sheet and for items cut or punched from sheet. ....