What Our Gearhead(R) Experts Are Saying:"I wore this through a hard bootpack where my heart rate stayed pinned near the top the entire way up. The eyelet mesh panels actually dumped heat where I needed it most, and the half zip meant I could vent instantly instead of stopping to strip a layer."A hard bootpack straight up a couloir turns any layer into a liability fast, overheating within minutes if it can't keep pace with the effort. The ZoneKnit Half Zip Top from Icebreaker is engineered for exactly that kind of intensity, zoned merino construction that channels heat away from the body precisely where exertion runs hottest. Eyelet mesh panels add breathability at key points without sacrificing warmth elsewhere, while a half zip allows instant venting the moment the pace picks up. A gusset underneath supports full mobility through high-reaching movement, and raglan sleeves paired with flatlock seams cut down on friction through the most repetitive motions of the climb. It's built for the effort, not just the layer underneath it.