Over or under. The insulating Arctic ML Jacket is the perfect cozy fleece to wear under a hardshell jacket and can also be worn as a breathable outer layer. The integrated Polartec® Thermal Pro® material has large pores and stores air that has been warmed by the body, which means it offers excellent heat retention. The material also dries extremely quickly after demanding ascents. The ideal heat/weight ratio, flatlock seams for extra elasticity and pre-shaped elbows make the Arctic ML Jacket a fleece for sporty winter pursuits.