B is a polymer block of a conjugated diene, the average molecular weight of the block being between about 15,000 and about 250,000; 3. the total blocks A being 10 to 35% of the total weight of the copolymer; B. 50 to 200 parts and preferably 95 to 140 parts by weight of tackifying resin or mixture of tackifying resins; C. 10 to 45 parts and preferably 15 to 35 parts by weight of a naphthenic plast