Mid-weight sock with silver yarn technology in the inner layer. Silver is proven effective as anti-microbial that kills 99.9% of bacteria associated with smelly feet. Silver technology also offers thermal conductivity and reflectivity properties keeping you comfortable in all weather conditions. Wrightsock patented Double Layer reduces the causes leading to blisters - friction, moisture, and heat - with and integrated system of two socks knit together. Sizing (All US sizing): Small- Womens 4-6, Mens (NA). Medium- Womens 6.5-9, Mens 5-8. Large- Womens 9.5-11, Mens 8.5-11.5. X-Large- Womens (NA), Mens 12-14.