The mountaineering experts at Arc'teryx believe that good design is the result of instinct, discipline and discovery. - The 'Phase AR' base layer is designed to withstand high output stop-and-go interval activities in cold temperatures - It's cut from mid-weight Phasicâ"¢ AR jersey that's engineered to provide optimum insulation - A combination of wicking and hydrophobic yarns will keep you comfortable during intense movement - Lighter weight Phasicâ"¢ SL panels improve thermal regulation - The collar is lined in fleece so it doesn't chafe, and the zipped front provides ventilation whenever it's needed Shown here with Arc'teryx trousers, Arc'teryx base layer, Arc'teryx boots, Bremont watch. - - Red Phasicâ"¢ AR - Fleece collar lining - Zip fastening - 100% polyester - Machine wash