The Vibram FiveFingers Spidrwalk is built around a 3. 7mm Vibram Megagrip outsole, a rubber compound developed for grip on wet rock, mud, and uneven surfaces where conventional outsoles lose purchase. TPU reinforcements protect the upper on rocky terrain without adding bulk, and the stretch polyester construction keeps the shoe lightweight and flexible enough to move naturally across variable ground. What Our Gearhead(R) Experts Are Saying:"The drainage perforations clear water fast enough that a creek crossing doesn't slow the pace. The shoe sheds what it picks up and dries out on the move, so the transition from riverbed to trail happens without stopping to deal with wet feet."