FDX brand new SLEEVELESS body Armour top improves blood flow and oxygen supply to your muscles and designed to regulate body temperature,wick moisture,dry quickly,control odour and improve the fit to enhance performance. High quality fabric which regulates your body temperature (meaning you are neither too hot nor too cold). Designed for maximum comfort and freedom of movement. This shirt is made of high quality 80% Nylon and 20% Elastane. Size Guide SMALL: 33" - 36" MEDIUM: 37" - 40" LARGE: 41" - 44" X-LARGE: 45" - 48 XX-Large: 49" - 52"