Sorel - Chieftan (Bistro) - Men's: Seam-sealed, waterproof full grain leather. Traditional metal eyelets with lace. Removable 13mm ThermoPlus felt InnerBoot. Removable 13mm Sorel Meltdown Midsole.; 2.5 mm bonded felt frost plug in the shell to provide an extra layer of insulation and warmth. Handcrafted, waterproof vulcanized rubber shell. Aerotrac sole (natural rubber). Sorel Rated: -100F/-73.3C.