With a drop tail hem that's easy to tuck into pants to seal up the potentially chilly gap there, the men's merino wool long sleeve Icebreaker Terrain Zip Bodyfit active base layer is a simple, natural, high performance cold weather base layer top. The Icebreaker Terrain Zip is a warm base layer shirt that has a self-fabric arm band strip for a bit of style, and itÆs made with Icebreaker Merino wool. Merino wool keeps New Zealand high mountain sheep comfortable and happy, insulating to warm them in the winter, and breathing and wicking to cool them in the summer and it works like this for active humans as well. The lightweight wool has ultra fine fibers so it feels soft and won't itch, and it resists static electricity build up so it won't cling. Icebreaker merino wool resists odor naturally so you can wear it for days or even weeks without washing it - and when you do, it's easy care: machine wash cool and line dry. For extra versatility the Terrain Zip from Icebreaker offers sun protection (UPF 50+ rating) so it works well as an outer layer, too.