Comfortable support with stockinette over orthopedic polyester felt. Sewn with zig-zag fashion for strength and flexibility under arm. Specify size (measure from center back, up over shoulder, around underneath arm, and back to center of back) Pediatric 10″-15″; Small 14″-20″; Medium 19″-28″; Large 24″-33″; X-Large 30″-39″.