This Proton Heavyweight Hoody is the warmest and most durable in the Proton series from Arc'teryx.  An air permeable mid or outer "active" insulation layer with abrasion and weather resistant outer fabric. A great choice for high output activities in colder temperatures when you are expecting a lot of wet weather on your outing.  Synthetic Coreloft™ insulation still retains the majority of its insulation value when wet.  These synthetic puffy jackets are more abrasion resistant than the Arc'teryx Atom series of puffy jackets, and are a superior choice for more demanding alpinists and mountain guides.