The Arc'teryx Men's Proton Insulated Pant warms up frigid alpine climbs with a performance-oriented design geared for staying active at high altitudes. Its air permeable Fortius Air 40 fabric delivers incredible breathability to keep comfy on long approaches and steep climbs, and it has a rugged . Octa Loft also promotes active-worthy breathability as well as thermal protection from cold temperatures. Arc'teryx fitted it trim to fit under hardshells, but you can certainly wear the pant on its own when there isn't much rain or snow.