Sierra Designs Nitro UL 20 Sleeping Bag Review

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Fully-opened zipper

Sierra Designs just launched their new Nitro UL 20 Sleeping Bag (available in 0°F, 20°F, 35°F, Women’s 0°F, and Women’s 20°F models) and we were fortunate enough to get our hands on a pre-launch model to test it out. We’ve been using the Nitro UL 20 for a few weeks now and we think it’s a solid offering in the sleeping bag world. The Nitro is comfortable, warm, keeps weight to a minimum, and is sold at a competitive price.

Note: Make sure to check out our Best Sleeping Bag & Quilt Guide for our top recommendations and critical considerations before buying a new sleeping bag.

Quick Specs

Sierra Designs Nitro UL 20 Sleeping Bag

Price: $339.95

Insulation: 800FP PFC-Free Dridown

Weight: 2.2 lb.

Listed Dimensions: ‎25 x 14 x 11 inches


  • Warm
  • Weight
  • Comfort
  • Fill
  • Zipperless footvent


  • Price
  • Zipper

Sierra Designs Nitro Specs


The Sierra Designs Nitro is available in three different temperature ratings (0°F, 20°F, 35°F, Women’s 0°F, and Women’s 20°F). Remember, temperature ratings like these are based on EN Lower Limit testing, so we recommend adding about 10°F for a more realistic estimate (read the temp rating sections of our sleeping bag guide for more info). For example, the EN “Lower Limit” of the Nitro 20 bag is 17°F, but it’s EN “Comfort” rating is 28°F, and the comfort rating is a much better guideline in our opinion. We tested the 20°F Nitro for this review and found it to be true to its temperature rating. For most 3-season backpackers we’d recommend the Nitro UL 20 model, which will keep you warm when temps dip to freezing or just below.


Quality down sleeping bags tend to cost a lot of money, which is a bummer. The upside is that they’ll last for decades if taken care of properly, but the upfront cost can be prohibitive for some. The Nitro isn’t an inexpensive sleeping bag, but it does deliver a lot of value compared to the competition. We wouldn’t list the Nitro as a budget bag, but there are very few sleeping bags in its weight, warmth, and cost class. For that reason, we think the Nitro is a solid deal. Check out current pricing for the Nitro UL 20 here.


Given its temp ratings and cost, the Sierra Designs Nitro is surprisingly competitive in the weight category. The 35°F regular size Nitro weighs 1lb 6oz, the 20°F Nitro weighs 1lb 12oz, and the 0°F Nitro weighs 2lb 8oz. These aren’t the lightest sleeping bags on the market, but they’re very competitive, and in our books this is a big win.


The Nitro comes with 800 fill DriDown insulation, which is a balanced choice for keeping weight down without decreasing compressibility and affordability. DriDown will help keep your insulation dry in wet conditions and will help your bag dry out much faster if it does get wet (but don’t let that happen). All in all, a well balanced choice.


In our view the Nitro has a comfortable and balanced fit. It’s not so tight that it feels claustrophobic and not so roomy that it feels drafty (which can create cold spots and cut down on warmth efficiency). The Nitro is offered in regular (fits up to 6′ tall) and long (fits up to 6’6″ tall and is a bit wider too) sizes, so make sure to choose the appropriate model for your height (we recommend going larger if you’re right on the edge). If you typically find sleeping bags to be too constricting, you may want to try a lightweight quilt for more freedom of movement, but quilts do tend to be drafty and a bit chilly at lower temperatures.


The Nitro has a 40 inch zipper, which runs a little past halfway down the bag. This is a key downside in our books, as we prefer the flexibility of full-length zippers. On warm nights it can be nice to fully unzip a sleeping bag and use it like a blanket, but that option isn’t really viable with a shorter zipper like this. Longer zippers do add weight and cost, which is probably why Sierra Designs kept the Nitro zipper shorter. Some sleeping bag users don’t mind a shorter zip, so if that’s you, the Nitro will be a great fit. Also, the Nitro does have a cool zipperless footvent (more info below) which helps with ventilation on warmer nights.


The Nitro has an ergonomic footbox that feels comfortable and kept our feet warm. The one truly unique feature of this sleeping bag can also be found in the footbox: a zipperless footvent. The zipperless footvent opening allows you to quickly stick your feet out of the bag whenever you’re feeling hot. We found this to be a nice touch and appreciated the ventilation. When not in use, the foot vent lies flat and holds heat in well, so we didn’t experience any unwanted drafts.


The hood of the Nitro has an ergonomic design and two drawcords that can easily be adjusted from within the bag. The draft collar near the hood opening also helps to hold heat in. The hood is simple, comfortable, and effective.


The Nitro is built with 15d shell and liner fabrics that feel comfortable against the skin and help keep weight down. The shell fabric feels durable, but like all lightweight sleeping bags, you’ll want to be careful around sharp objects.


The Nitro has a draft tube (down-filled flap) that runs the length of the zipper and a draft collar around the neck of the bag. These draft tubes help hold heat in, which increases warmth efficiency and reduces cold drafts. Both are nice touches. 

Summary of Pros

  • Warm: 3 EN-tested models that are true to their temperature ratings.
  • Price: Good value, especially considering overall weight and quality materials.
  • Weight: Very competitive weight to warmth ratios.
  • Comfort: A slightly relaxed mummy cut with fabrics that feel nice against the skin.
  • Fill: 800 Fill DriDown insulation. A balanced choice for weight, cost, and compression.
  • Zipperless Footvent: A convenient new feature that helps with temperature control.

Summary of Cons

  • Price: Though a good value, the price may still be too much for budget backpackers.
  • Zipper: We prefer full-length zippers for maximum flexibility on warm nights. The Nitro has a 40-inch zipper, which runs about 1/2 to 2/3 the length of the bag.

Bottom Line

We think the Sierra Designs Nitro UL 20 is a solid new offering in the sleeping bag world. It’s comfortable, warm, keeps weight to a minimum, and comes at a competitive price, especially given the quality of its construction and materials. We wish it had a full-length zipper, but the zipperless footvent is a nice feature that helps increase ventilation on warm nights. If you want to see how the Nitro stacks up against some of our favorite sleeping bags, check out the CleverHiker Sleeping Bag Gear Guide.