This review is for the women’s version of Nemo’s Rhythym 40 bag, which is called the Harmony 40. 

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 Harmony gets middling grades on compressibility.

Warmth
Rated to 40ºF by the manufacturer (not the 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 Harmony moved to the bottom of the rankings in the warmth-to-weight ratio.

Comfort
The Harmony 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.