Never trust an atom, they make up everything, funny life science joke for teachers and professors! Unisex Shirt for Men or Women: an everyday favorite. 100% ring-spun cotton (Sport grey is 90% ring-spun cotton+ 10% polyester, Dark heather is 65% polyester+ 35% cotton, Fabric weight: 4.5 oz/y² (153 g/m²). Pre-shrunk for extra durability