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. Gen III Level II Underwear bottom - Black.