Description of Hot Chillys MTF4000 Crewneck Top Moisture transport to keep skin dry and to promote warmth, Bio Del Mar Antimicrobial polyester used in high moisture areas for odor control, Blend of Eco-MTF, recycled polyester and MTF micro polyester, Lightly sanded face for softness and warmth. Features: Eco MTF recycled polyester blend MTF polyester yarns Spandex Contoured body fit Soft cotton feel Flat seam construction for seam strength and to eliminate abrasion UPF rating of 30+ Warmth Factor = 7