Sand Gen III Level Ii Underwear Bottom is made up of polyster/Spandex. With microban. Anti-microbial. Anti-odor defense. Breathable, moisture-wicking grid fleece. Elastic waist. ECWCS - Extended/Extreme Cold Weather Clothing System. Military thermal bottoms. Lightweight. Can be worn alone or as a base layer for extra warmth. GI - Government Issued style. Army style. Military style. GEN III. GEN 3. Thermals are great for skiing, camping, hiking, hunting, sleep wear, cold conditions, and much more.