Montane Aero Cap. Designed for the high activity trekker or runner, the Aero is a high performance outdoor cap which provides sweat absorption, eye protection, sun protection and moderate warmth. Tactel Dynamic: for wind and water resistant stretch fit over the crown. Dryactiv Express: for high breathability on the side panels. If your serious about your outdoor trekking then this is a great solution to keeping your head warm.