A thin, crew length liner sock based on the Finnish military ‘heat condition’ sock, UpHillSport “Contact” Tactical L1 Liner Socks are best used solo to protect feet and ankles in warmer temperatures, or combined with an outer sock as a layer when the thermometer drops. The sock design includes a fitted heel, a seamless toe to prevent the rubbing that leads to blisters, a supported arch to grip and keep the socks in place, and ventilation at the top of the foot for breathability and moisture control. They have an antibacterial treatment to help keep the feet fresh.