The KSO is arguably Vibram's most successful FiveFinger to date, mainly due to its versatility. Having been added back into the mix a few years back to celebrate the rebirth of a legend. When you're scrambling up a rocky bluff or bounding along a riverbank, the last thing you want is gravel and grit seeping into your FiveFingers. So why not Keep Stuff Out! The KSO has a snug fit, one of the most minimal sole constructions for maximum ground feel, and a breathable, quick drying upper. The KSO also features a thin, abrasion resistant stretch polyamide and breathable stretch mesh that wraps your entire foot to do just that. A single hook-and-loop closure helps secure the fit. Non-Marking XS Trek performance rubber soles are razor-siped for sure grip.