Strongly enhanced GMR on flexible substrates is reported for (Co_1 nm/Cu_1 nm)(N) multilayers deposited on plastics (P) by introducing a photoresist (PR) buffer layer. GMR values of Co/Cu multilayers on buffered flexible substrates are even larger than those on thermally oxidized Si (Si) substrates due to an increased antiferromagnetic coupling fraction. The GMR effect can be easily tuned mechanically by substrate stretching.