West's 5mm mitten is a serious cold water glove. Made out of a 100% Ultraspan neoprene, which is a non-petroleum, limestone based SUPER stretchy neoprene for maximum mobility, warmth, and flexibility.The seams are triple glued and blind stitched and then sealed with Fluid seam technology (liquid tape). West's limestone based neoprene comes from a distinct region in Japan and is warmer, lighter, strechier, and softer than petroleum based neoprene. Most importantly, it is environmentally friendly!