When folded into its stuff sack, this Pertex windshirt is the size of a small apple and weighs only about 100g. Unlike a “real” coat, the smock can disappear into a jacket pocket or cargo pocket of your combat pants or it can lurk, weightlessly, for weeks in a backpack until needed. Other than being a carry-all-the-time item allowing minimal bulk, it’s extremely versatile. It blocks the wind, preventing windchill, while still feeling as breathable as a lightweight cotton t-shirt. Pull up the neck zip and the smock will trap a layer of air around your body. Because the smock keeps this air dry instead of letting it saturate with sweat, it’s a superb insulator: the ground outside has been white with frost recently, but I’ve been quite happy walking around with the smock over my sweater (about 0 Centigrade). Shower resistant, but not waterproof, it’s much more breathable than anything I’ve tried that is waterproof — while Goretex may transmit about 25% of water vapour in even ideal circumstances, Pertex scores closer to 100%. As such, the windshirt is a great outer layer for hikers, cyclists and runners to wear in all conditions where real rain wear isn’t essential. It’s also terrific for commuting and tourism, especially when added to a light umbrella, which allows you to leave heavier-to-carry and sweatier-to-wear just-in-case clothes at home. I have read that if you soup up the water resistance with Nikwax DWR, it makes an acceptable waterproof, but I haven’t tested this. Serious outdoor adventurers in serious conditions might want to look at the Featherlite’s grown-up, bulkier, heavier cousins like the Montane Extreme, Paramo, and especially various Buffalo products. These combine Pertex with insulating material to provide single-layer high performance clothing for skiing and mountaineering in very harsh conditions. Other brands like Paramo and Marmot offer products similar to the Featherlite. I went with Montane because of their reputation. They’re the kings of ultralight, which is what this type of windshirt should be about.