The unique ingredient in these socks is the Polygiene technology. Made with low concentrations of silver salt, which has anti-microbial properties and is naturally present in water and soil, to safely eliminate the ability for bacteria and fungi to grow. This is only active on the sock itself and does not interfere with the skins bacterial flora. The added benefit of Polygiene odour control will not wash out as the technology is bound and permanently integrated into th sock. The Marathon Fresh is also made with LYCRA SPORT fibre to ensure a close, comfortable fit.