Personalized 40 Rocks 40th Birthday T-Shirt. Pink butterfly with 40 Rocks on a 40th Birthday T-Shirt - White gift. Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.