Duofold Polypropylene Mid-Weight Long-Sleeve Kids' Crew Shirt # 232D base-layer-underwear closure Single-layer polypropylene fabric provides toasty warmth without weight. Better yet, it wicks away m Allover ribbing adds natural stretch, for sleek fit and freedom of movement. Details add durability: neatly bound crewneck; cozy ribbed cuffs; non-chafe reinforced seams. 100% polypropylene