NEMO Rhythm 25 Sleeping Bag
Temperature Rating 25F / – 4C
- Fill Type: PrimaLoft® Synergy
- Fill Weight: 24 oz / 666 g
- Minimum Weight: 2 lbs, 12 oz / 1.2 kg
- Spoon Shape
- Shoulder Girth 64 in / 162 cm
- Hip Girth 60 in /152 cm
- Knee Girth 68 in / 172 cm
- Packed Size: 14 in x 10 in / 36 x 25 cm
- Compressed Volume: 10.4 L
- Shell Fabric: 40D Nylon Ripstop + DWR
- Footbox Fabric: 15D OSMO™ DT W/B + DWR
- Lining Fabric: 30D Nylon Taffeta
Locations Tested: Sangre de Cristo Mountains, Jemez Mountains, the back of my truck
Nights Used: ~30
Temperature Range Used In: 23 F – 47 F
As someone who’s never been very happy with the comfort of mummy bags, I wanted to see how NEMO’s “Spoon Shaped” Rhythm 25 bag compared to the warmth, weight, and packability of a mummy bag in a shape that was allegedly more comfortable to sleep in.
Rather than placing the widest point of the Rhythm 25 at the shoulders, then tapering down to the footbox (as with a mummy bag), the bag has an hourglass shape, with the narrowest section of the bag around your waist. The design is meant to provide more real estate for your lower legs and feet, allowing for more natural, comfortable sleeping positions.
In NEMO’s words: “Our revolutionary Spoon Shape strikes a balance between the performance you want on the trail and the comfort you want in camp. It’s generous at the elbows and knees, where you need it for side sleeping.”
My experience sleeping in the Rhythm 25 is consistent with NEMO’s claims about their Spoon Shape. I’m a stomach/side sleeper, and the Rhythm 25 gives me plenty of room to move around during the night. I’ve yet to wake up in the morning cocooned in a twisted mess of a sleeping bag.
The only bag I find more comfortable is my rectangular Coleman bag. It’s Flannel-lined with a canvas exterior, so life doesn’t get much better when it comes to camping comfort. But it weighs over 40 lbs (!!!), so it’s out of the question for backpacking, unless your trekking partner is a llama.
All bags in NEMO’s Rhythm series are stuffed with Primaloft Synergy synthetic fill, and those in their Nocturne series have the same spoon shape but are filled with down insulation. Synthetic fill technology has come a very long way in recent years, but it doesn’t quite offer the same packability and warmth-to-weight ratio of down. Stated weights for NEMO’s 15 and 30 degree Nocturne down bags are 6oz and 12oz lighter respectively than those in the Rhythm series, and the stated compressed size for the down bags is close to half that of the synthetic fill versions.
However, compared to down, synthetic will do a much better job of maintaining its loft and providing insulation if it gets damp. In the high desert of New Mexico, when I’m really not expecting much in the way of precipitation, a synthetic fill bag isn’t my first choice. But if I were going to be doing a lot of cold, damp fall/winter backpacking in the Cascades, I would absolutely opt for a bag from NEMO’s Rhythm series.
The Rhythm 25 is a synthetic bag and packs like one. It’s not as compact or light as a down bag. However, the Rhythm 25 is also available with down fill, so you’re not out of luck if you like the sound of the bag’s shape and its features (which I’ll get to in a moment).
For the most part, the Rhythm 25’s 25° F temperature rating seems accurate. I’m not an especially “warm” or “cold” sleeper, but I did have to add a layer or two to remain comfortable as temps got down into the mid 20s. I would keep this in mind if you do tend to run cold and plan to use the bag often in temperatures around 25°F.
One of the reasons mummy bags were developed was to minimize excessive air circulation, which creates cold spots, thus optimizing a bag’s thermal efficiency. But the Rhythm 25’s spoon shape still seemed to do this well, especially while I was sleeping on my side or stomach when my shoulders/arms and legs filled in the added space at the top and bottom of the bag. When sleeping on my back in a mummy position, I did notice that the edges of the bag adjacent to my knees were not used efficiently, but since I spend about 2% of my time in a sleeping bag in that position, I’m willing to live with this trade-off.
In this way, the Rhythm 25’s shape lets it strike a really nice balance between the good thermal efficiency of a mummy bag and the comfort of a big, roomy, rectangular bag.
There are a couple of design elements and features I’d like to touch on, starting with the bag’s headbox, the “hooded” portion of the bag that surrounds your head.
Relative to a more traditional mummy bag, the headbox on the Rhythm 25 is wide and shallow. It accommodates my head well when I lie on my side, but the headbox’s draw cord sits pretty snugly right against my forehead when I’m on my back, which is somewhat uncomfortable. The wide shape of the Rhythm’s headbox also makes it harder to get a good, tight fit around your face, as with traditional mummy bags, in order to best retain heat in the bag. This, however, is helped by another feature of the Rhythm 25, the “Blanket Fold.”
The Blanket Fold is a panel of material that’s attached to the opening of the Rhythm 25 below the headbox that lets you “pull the sheets” up around your neck for a really familiar cozy feeling. Tucking the Blanket Fold into the headbox around your shoulders also helps to trap the heat that can escape from the bag as a result of its wider headbox.
I noticed that frost can accumulate on the edge of the Blanket Fold (from your breath on cold nights) if it happens to work its way outside the bag—a bummer when you then pull it back in around your chin. I’d love to see NEMO conceive of a way to secure the Blanket Fold in place so it doesn’t flop to the outside of the bag during the night. I’d also like to see it built just a little bit wider toward the loose end to better fill voids in the headbox opening.