As good as todays pile and fleece jackets can be, they still dont pack the warmth-to-weight ratio of insulated shells&$151;that is, pieces that have down or synthetic insulation wrapped inside a very light, (usually) nylon shell. Theyre simply loftier than fleece, and loft equates with better heat retention. The extra shell also cuts down on wind and evaporative cooling (the heat lost when moisture on the skin evaporates). And, their shell makes them great layering piecesan outer shell such as a Gore-Tex jacket can slip right over them.
But, what to go withdown or synthetic? Western Mountaineerings new Flight Jacket ($199; www.westernmountaineering.com) uses high-quality 850-fill down to create a very warm piece thats still very light, only 10 ounces! And its a lot of jacketthe Flight actually could be seen as a very light down parka. Bozeman Mountain Works Cocoon Pullover ($179; www.bozemanmountainworks.com), on the other hand, uses Polarguard Delta, the newest iteration of that long-popular synthetic fill. Its even lighter than the Flight (8.5 ounces) but achieves that in part by eschewing features such as a full zip.
Other solid candidates include Moonstones very fine Lucid Down Jacket ($160; www.moonstone.com) or Patagonias synthetic-fill Micro Puff Pullover ($148; www.patagonia.com), which are each similar to the Flight and the Cocoon in features and warmth. I use a Micro Puff as a skiing base layer and love it.
Still, for backpacking, Id go with a down piece, either the Flight or the Lucid. I just prefer downits warmer for each ounce of fill than synthetic. Its also softer, packs down more easily, and lasts longer. The two downsides are cost and water-resistance. But cost isnt really a factor here as both down pieces are competitive with synthetic. So what about the water angle? Its true that down can wet out, at which point it takes forever to dry and doesnt offer much insulation during that time. But when it rains you were a waterproof shell, right? And even if down does get damp, it takes quite a bit of water to really remove its insulation value.
So go get the Flightor the Lucidand stay warmer.