This British Standard specifes compositional and physical property requirements for four non-black
natural rubber compounds designated R40, R50, E60, R70, three non-black natural rubber/zinc oxide
compounds designated S40, S50, S60 and five black natural rubber compounds designated T40, T50, T60, T70, T80.
These compounds are intended for the manufacture of items in the form of extrusions and items cut from extruded sections, e.g. washers.