PI DAY Tshirt with Funny Pi Cartoon Solid colors: 100% Cotton; Heather Grey: 90% Cotton, 10% Polyester; All Other Heathers: 50% Cotton, 50% Polyester Imported Machine wash cold with like colors, dry low heat Pi Day is celebrated on March 14, because....pi. Celebrate Pi Day with a cute Pi cartoon tee. Lightweight, Classic fit, Double-needle sleeve and bottom hem