The jersey knit fabric level-1 of the E.C.W.C.S. System helps provide extra warmth in cold climates. Frank Bee silk weight underwear top is highly breathable, with moisture-wicking properties and features anti-odor properties. The level-1 underwear top also has a long back tail and thumb-hole sleeves. It great for layering in the wintertime and works well with our other ECWCS items or underneath t-shirts, jackets and more.