icebreaker's slim-fitting Merino 260 Quantum Long-Sleeve Zip Hoodie provides comfortable insulation for fall hikes and winter ascents, thanks to its techy full-merino wool composition. Whether we're layering this midlayer under a ski shell or donning it over a technical tee for a cool-weather hike, the temperature-regulating and moisture-managing properties of merino wool offer warmth while we work and prevent us from sweating out. icebreaker updated the shape of this iconic jacket to offer greater arm mobility and reduced chafing while traveling with a pack.