And the details are designed for movement so it is an ideal baselayer under a top or shell and great for wearing alone on a cool morning run or a hike in the mountains flatlock seams won39t chaffe a drop hem for more coverage and set in sleeves keep it comfortable under a pack if you get too hot the half zip provides instant ventilation and because it is merino you can wear it several times between washings odour free why icebreaker merino the merino is an ancient breed of alpine