gram fabric that holds heat through long days in genuinely cold conditions. Shoulder panels remove the seam that usually sits under a pack strap, and flatlock construction keeps every seam flat against the skin through repeated motion. The quarter-zip vents heat the moment the pace picks up, then seals it back in as soon as the wind returns. What Our Gearhead(R) Experts Are Saying:"I run the zip down on the climb and seal it tight the second I stop moving, and this top handles both without ever feeling clammy against my skin."