Stretch-fit topline binding keeps warmth in and cold out. 5 mm (millimeter) CR flex-foam bootie with 4-way stretch nylon. 100% waterproof, lightweight and flexible. Comfort range: Sub-freezing to 85 degrees. Triple reinforced in the toe area and quadruple reinforcement in the heel area. Additional Achilles reinforcement for added protection. Steel shank for additional arch support.