Breathability
The Arc’teryx Proton AR Hoody stretch woven nylon “Fortius Air 40” outer fabric and “Permeair 20” ripstop nylon inner fabric provide a level of breathability suitable for moderately intense activities like rock climbing and hiking in near freezing conditions. The jacket’s air permeability is challenged with intense aerobic pursuits in temperatures above 40F.

Durability
The exterior fabric of the Arc’teryx Proton AR Hoody is very robust, battling off rough rocks, broken branches and pack straps without issue. The stretch knit, gusseted cuffs have no Velcro to wear out and the inner fabric is snag resistant while still having an open, air permeable structure. The only suspect component are the tiny, hidden zippers used for the two chest pockets although no problems arose during the testing period. The quality and care of construction is evident upon close inspection of the jacket, with all stitching amazingly tight, straight and uniform. 

Weatherproofing
The Arc’teryx Proton AR Hoody’s wind resistance proved excellent, warding off moderately piercing winds with just a hint of airflow. The main zipper has a tiny draft flap behind each side that blocked moderate winds. The DWR treatment of the outer shell is also one of the more impressive performers in this test, keeping water entry at bay during a steady light shower. This jacket is one of the warmer ones in this test, comfortable at near freezing temperatures. The hood’s insulating ability rivals that of the body, providing excellent warmth for the head and neck. 

Fit/Comfort
The Arc’teryx Proton AR is trim in all dimensions but still provides great freedom of movement. The slightly elastic shell fabrics, underarm gussets and articulated elbows do an incredible job of allowing full arm movement without the lower hem rising up or the shoulders becoming constricted. Torso girth is adjustable through two lower hem cord locks. The front of the torso doesn’t stay tucked into a climbing harness but the longer drop hem on the rear of the torso does. The brimless, elastic bound hood fits over climbing helmets and is adjustable through one rear mounted cord lock. It moves well with the helmet, with just a touch of binding at the extremes of head rotation. Layering underneath is limited to midweight base layers and both inner and outer fabrics glide well against other pieces but is a bit sticky against bare skin.

Compressibility
The Arc’teryx Proton AR will shrink down to the size of a cantaloupe. The “Coreloft Continuous 90” and “Coreloft Continuous 65” insulation has a high level of rebound. 

Features
The Arc’teryx Proton AR has a minimalist, but usable feature set: two zipped handwarmer pockets (will not clear pack hip belts), two zipped, stretchy chest pockets (fits cell phones), and a “No Slip Zip” main zipper (bumps at the top of the zipper keep it from inadvertently opening). One minor ding: all the zipper pulls are small and hard to operate with cold or gloved fingers.