Lighter than the original and with the same features as the hoody by the same name (minus the hood, of course), the Atom SL Jacket is one of the most useful (and packable) pieces you can own. Wear it as a standalone layer when trail runs take you through cold, wet weather or layer it with a waterproof shell when mountain pursuits demand additional warmth and mobility. Breathable and weather-resistant, it has stretch insulation in the body but not the sleeves — maximizing packability while still delivering focused warmth to your core. Need a heavier option? Try the Atom Jacket .