an elastomeric composition comprising an elastomer matrix having dispersed therein about 3 - 30 parts per 100 parts by weight of the elastomer of powdered polytetrafluoroethylene having a number average molecular weight of at least about 250 , 000 and a surface area of at least 1 m 2 / g which has been treated with about 50 - 120 % of sodium - naphthalene addition compound or another addition compound of an alkali metal required for the alkali metal to react with all the fluorine atoms on the surface of the polytetrafluoroethylene powder . by dispersing such treated polytetrafluoroethylene powder in elastomer matrix , one increases significantly the tear strength of the elastomer , while increasing its modulus only moderately . in this way , the processability of the elastomeric compositions is not adversely affected .