The Military Issued USMC FROG (Flame Resistant Organizational Gear) is a Cold Weather Base Layer Thermal shirt that is part of the military cold weather clothing system (ECWCS). Manufactured by XGO for the USMC, it was designed to be a base layer thermal shirt worn next to the skin to wick perspiration and keep you warm while also being no-drip-no-melt flash fire resistant for safety. Base Layer Thermals are used in all layering system and pair with the F.R.O.G Grid Polar Tec Fleece or any mid layer. A perfect thermal shirt for those not just in combat but everyday work and active use especially where no-drip-no-melt is a safety need. Silk Base Layer Thermals are best worn snug so when temperatures drop you can layer over it and can be sized down. USA made; FROG Thermals have proven to work.