Pi Day of The Century - PiDayShirt 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 of The Century - PiDayShirt Lightweight, Classic fit, TearAway label, Double-needle sleeve and bottom hem pi day shirts, pi day 2015, pi day 2016, pi day of the century, pi day t shirts, ultimate pi day 2015, pi day t shirt 2015 4.5 oz 100% Combed Ringspun Cotton, machine wash cold with like colors, dry low heat