The shirt is made from Nike's well known Dri-FIT material, that keeps sweat from the body - to keep you dry and comfortable. it works by evenly distributing the sweat and moisture across the material, improving the efficiency of the body own cooling system.
Furthermore it has large panels of mesh, under the armpits and on the back to increase breathability. When you train hard, the back is where you sweat the most. Nike has therefore designed a special mesh zone on to ensure airflow on the back.
The t-shirt is designed to sit tight on you, making it feel like a second layer of skin - as the material is flexing and moving along with your own skin . Made from 89% polyester and 11% spandex.