You don't need to be an engineer to understand efficient heating: Small spaces are easier to warm than large ones. The compact Sub Kilo (57-inch girth) relies on that basic rule to deliver a tiny-packing bag that has features, like a full-length draft tube and zipper, found on bulkier sacks. We also liked the weather-resistant Pertex microfiber shell, but treat it gently--we saw scuffing after a night on slickrock. Downside: There's simply not enough of the 700-fill-power down in the baffles and hood, leaving two testers dodging cold spots when temps dipped into the 20s.
Rating: 20-degree F
Sizes: 3 sizes
Weight: 2 lbs. 1 oz.
Contact: (800) 426-4840; www.rei.com.