Under Armour Men's O Series Relaxed Crew Undershirt Tops Fit: Fitted--Close-to-body, contoured fit for maximum performance. Fabric Type: Stretch--Usually a blend of knit or woven fabric with spandex or elastane. Creates a soft, durable fabric which allows freedom of movement yet retains its shape through repeated wash cycles. Performance Technology: Under Armour HeatGear --For when it's hot. HeatGear technology wicks perspiration off your skin, rather than absorbing it. It's engineered with UA's Moisture Transport System to deliver core temperature regulation and maximum breathability. Ventilation--Mesh or breathable fabric inserts in high heat zones allow sweat to evaporate and cool air to circulate. Fabric Content: 90% polyester, 10% elastane