The Genuine Issue USMC FROG (Flame Resistant Organizational Gear) Long Sleeve Top is a Cold Weather Silk Weight Thermal shirt that is part of the cold weather clothing system (ECWCS). Designed to be a base layer and worn next to the skin, it wicks perspiration and keeps you warm. FROG base layer thermals should be worn snug so when temperatures drops you can layer over it with the F.R.O.G Grid PolarTec Fleece, USA made and manufacture to resist sparks and not melt from high heat making them both warm and safe for both work and combat missions.