Level Two of the ECWCS (Extended Cold Weather Clothing System) Rothco's Mid-Weight Thermal underwear bottoms are an essential base layer for military and tactical professionals. The highly breathable, moisture-wicking polyester and spandex material is designed to protect from the harshest elements. Rothco’s mid-weight underwear bottoms feature an elastic waistband and access fly. Rothco's base layer underwear bottoms feature a grid fleece fabric which is anti-odor for long-lasting wear.