White sidewall for pneumatic tires

A butyl-type rubber composition comprises 70-90 parts of a copolymer of an isoolefin of 4-07 carbon atoms, e.g. isobutylene, with an open chain conjugated diolefin of 4-8 carbon atoms, e.g. isoprene, 30 to 10 parts of a chlorosulphonated polythene and 105 to 130 parts of a reinforcing filler comprising 15 to 40 parts zinc oxide, 20 to 47 parts titanium dioxide and 30 to 50 parts silicon dioxide, all parts based on 100 parts of copolymer and chlorosulphonated polythene. The composition may also comprise magnesium oxide, stearic acid, ultramarine blue, paraffin wax, a light mineral oil and a polyhydric alcohol ester of hydrogenated rosin and may be vulcanized with sulphur, tetramethylthiuram disulphide and 2-mercaptobenzothiazole, e.g. to a tyre to form a white sidewall or a barrier-strip to prevent white sidewalls being stained by additives in the tyre.