The Mountain Fly has been designed and engineered to protect your feet from pretty much anything. A GORE-TEX membrane in the upper adds breathability while also providing industry-best waterproofing. Where there's no GORE-TEX material, durable hard rubber keeps everything else at bay. That same hard rubber wraps up around your big toe for over-the-top protection and uses thick, chevron lugs on a sticky outsole for maximum grip and propulsion. A flexible ankle cuff keeps out unwanted debris, while reflective design elements on the heel and lace cover help with visibility at night. The secret sauce sits in the comfy React midsole, where a carbon-fibre plate taken from the cutting-edge Vaporfly 4% runs the length of the shoe to add stiffness for endurance while protecting you from hard, uneven surfaces.