Under Armour Boys Base 2.0 L/S Crew (Big Kids) Imported Machine Wash Constructed of 93% polyester, 7% elastane fabric. UA Base 2.0 is highly versatile mid-weight protection for colder conditions and a variety of activity levels. Soft, brushed negative grid interior traps hot air, providing superior warmth. Four-way stretch fabrication allows greater mobility and maintains shape. Signature Moisture Transport System wicks sweat away from the body.