While Therm-a-Rest no longer makes this bag, we do continue to put out updated ultralight sleeping bag reviews.
The Therm-a-Rest Navis is the company's lightest sleeping bag. It saves weight by omitting a zipper, eliminating insulation from the bottom of the bag, and by not having a hood. Two elasticized mesh straps secure the bag to any sleeping bag up to 25 inchs wide. Unfortunately, the bag weighs more and is colder than than many other sleeping bags we've tested. This is also the least comfortable and least versatile sleeping bag tested.