Compressibility
The unique shape improves comfort, but does add extra materials to the bag to accommodate those flared sections. That means more ‘stuff’ to stick into a stuff sack. The Primaloft insulation compresses better than some other synthetics, though, so the Rhythm gets middling grades on compressibility.

Warmth
Rated to 40ºF (by the manufacturer, not a standardized EN rating), I discovered I was comfortable even into the upper 30s. A few of my colleagues, though, said they had to pull on a jacket during nights that dipped into the low 40s. For a bag that tips the scales at nearly 3 pounds, the Rhythm moved to the bottom of the rankings in the warmth-to-weight ratio.

Comfort
The Rhythm makes up for that low grade with a stellar score in comfort, however. The “spoon shape” features a little extra width in the shoulders/upper torso—it narrows through the hips and waist, while a flaring around the knees. This shape alleviates pressure points when you twist onto your side, with your knees partially drawn up. The shape proved a winner with our team, even those who don’t regular sleep on their sides. The extra spaces do allow some wiggle room that makes sleep comfortable even for back-sleepers. The extra spaces do allow some dead-air spaces to draw off heat, though, so the bag can be cool at times.

Durability
The 40-denier ripstop nylon shell and 30-denier lining held up well to use and abuse, and the bag showed no loss of loft after that use and two machine washing cycles.