"The Patagonia R1 Air Jacket is built for the moments when a standard fleece becomes a liability: the sustained climbing pitch, the skintrack, the long ridge traverse where output stays high and stopping isn't an option. The jacquard weave and hollow-core yarns dump heat and moisture faster than a solid-knit fleece, so the slim fit stays comfortable against the skin instead of clammy. The hip length and single chest pocket keep the profile clean under a harness or a shell. What Our Gearhead® Experts Are Saying:""I wear this on the approach and keep it on through the crux. The hollow-core yarns move heat out fast enough that it never turns into a sauna under a shell."""