This British Standard specifies compositional and physical property requirements for four rubber compounds based on either isobutene-isoprene (butyl) or halogenated isobutene-isoprene (halobutyl) of hardness ranges 50 IRHD to 80 IRHD, designated B50, B60, B70 and B80.
These compounds are intended for the manufacture of items in the form of extrusions, mouldings, moulded or calendered sheet and for items cut or punched from sheet.
NOTE The compounds do not necessarily have good electrical insulating properties.