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Updated Aug 2, 2022 7:33 AM

If you’re like me and hate a heavy backpack, then you probably already know that the heaviest three items are typically the backpack itself, your shelter, and your sleep system, so we’re going to focus today’s review on shaving ounces and finding the best ultralight sleeping bag for you. 

Ultralight (UL) backpacking is more of a state of mind than a specific definition. It’s about taking a serious look at how much every item of your gear weighs and making decisions about whether to take it or replace it with a lighter option. It also involves understanding what you’re sacrificing in terms of trade-offs. In order to go fast and light, hard decisions have to be made and frequently you’re giving up a bit of comfort, versatility, and/or durability over heavier similar items. 

Any idiot can make a heavy sleeping bag. Sure, it will be warm, but it will also be bulky and weigh a lot. It takes real talent to make sleeping bags light, warm, and compressible or packable. Typically, this is done by making the sleeping bag more form-fitting to the body (less interior volume equals less material equals less weight), using stronger, lighter, and more often less durable materials (10 denier fabrics or lighter), shortening zipper lengths (full to half or one-third), omitting add-ons like interior pockets, and using the very highest quality down (800 power fill or higher). 

So strap in and let’s find the best ultralight sleeping bag for you!

Therm-A-Rest is known for making top-quality sleeping pads, and the Hyperion 32 is a great mate to its NeoAir XLite sleeping pad, which I’ve used for years. Like other top-end makers, Therm-A-Rest uses the latest in material technology to provide an exceptionally light and packable bag. It’s warm enough for late spring, summer, and early fall use, and users should note that the bag is comfort rated at 41F and marketed as a 32F bag. The bag is filled with 8.5 ounces of 900 power fill down — the best on the market. The bag lofts quickly and uses box baffle construction to keep the down fill where it needs to be to avoid cold spots and keep you warm. To maximize warmth and save weight, the designers put 70 percent of the insulation on the top of the bag and 30 percent on the back. This may be an issue for side sleepers. The hood of the bag is cinchable and has a nice draft collar. The snag-resistant two-way zipper runs just over half the length of the bag. While it saves weight, it also prevents the option of ventilating the bag below the knee. Therm-A-Rest also ingeniously integrated two removable sleeping pad straps that keep you from sliding off your sleeping pad in the middle of the night. Genius!

Remarkably, this bag is one of the lightest on the market, and Therm-A-Rest shaved ounces by making the bag very form-fitting. I’m 6-foot-3 and tested the long variant of the bag. I felt snug but not overly constrained in the bag. The footbox was roomier and more comfortable than my current UL sleeping bag, the Marmot Hydrogen 30 bag. With the help of a well-designed lightweight stuff sack, it packed down incredibly small — just a bit larger than a one-liter Nalgene bottle. This is a high-quality, high-performance, two-season bag for fast and light missions. It also comes in a 20F variant.

Product Specs
  • Weight: 16 ounces / 460 grams
  • Fill: 900 down
  • Fill weight: 8.5 ounces / 250 grams
  • Warmth
  • Comfort: 41F
  • Limit: 32F
  • Extreme: 5F
  • Packed dimensions: 5.5 x 6 inches
  • Materials: 10D nylon ripstop shell with DWR finish
PROS

Incredibly lightweight

The very highest fill power hydrophobic down

Very compressible, packable

Thermally efficient baffled box construction

Integrated sleeping pad hugging straps

CONS

Expensive

Warmth rating is a bit hyped

My very first sleeping bag was a synthetic insulation 30F made by Sierra Designs. I love this bag even more. First, because of its design and use of high-quality 800 power fill down, it compresses down to about one-third of my old synthetic bag and weighs pounds less. The shell of the bag is durable 15D water-repellent ripstop nylon and the lining is also 15D nylon. The mummy cut of the bag and baffle design reduce weight and also makes the bag more thermally efficient.

One of the tradeoffs of this bag is that the designers built it with a half-length zipper to reduce weight, but this decision also limits some versatility in ventilation below the waist. Sierra Designs did find a lightweight and creative solution to lower body ventilation by designing a self-sealing foot vent, which adds a bit of weight, but I think it’s worth it for the increased versatility in venting. The zipper does have a large hanging draft tube to keep out cold air and also features anti-snag material along its run.

The bag weighs in at a pound and a half and the non-compressible stuff sack is about 13 by seven inches. I highly recommend getting a compressible stuff sack to further reduce the mass of this bag to increase packability. If you feel restricted in mummy bags, consider Sierra Designs’ Nitro Quilt 35 at 22 ounces (620 grams) and $249 — essentially an oversized down comforter in ripstop nylon.

Product Specs
  • Weight: 22 ounces / 623 grams
  • Fill: 800 down
  • Fill weight: 9 ounces / 255 grams
  • Warmth
  • Comfort: 37F
  • Limit: 27F
  • Extreme: NA
  • Packed dimensions: 13 x 7 inches (without compression sack)
  • Materials: 15D nylon ripstop shell, 15D liner
PROS

High-quality 800 fill power hydrophobic down

Draft collar to seal in heat

Sidewall baffles prevent down shifting

Innovative self-sealing foot vent

Anti-snag zipper

CONS

Stuff sack lacks compression straps

Half-length zipper

Editor’s Choice

The Magma is REI’s top-end ultra lightweight series of sleeping bags. It comes in 30F and 15F versions. The Magma 30 features a high-tech 15D Pertex shell, supple 15D nylon lining, and is sandwiched between almost 10 ounces of high-quality 850 fill power down. It’s cut a bit more roomier than many UL bags, especially at the knee and foot. Starting at the top, the contoured hood is more form-fitting than most and features two different hood drawcords to allow you to dial in comfort. The insulated collar yoke is generous and prevents cold drafts at the neck and shoulder.

Unlike many UL bags, the Magma features a full-length zipper that allows for more ventilation options at the cost of a few more grams. They’ve redesigned the zipper cover and added an internal anti-snag strip to keep the nicely designed zipper pull from fowling. The design of the zipper allows for fast and easy unzipping, which is key when you need to pee in the middle of the night. The bag also features a zipper pull garage to prevent it from bothering your face. Variable baffle spacing helps eliminate cold spots and keeps the down fill from shifting around.

My only gripe about this bag is that it is marketed as a 30F bag but really has a 39F comfort rating, so it should be marketed as a 40F bag. It could benefit from another ounce or two of down. Also, it doesn’t come with a compressible stuff sack.

Product Specs
  • Weight: 19.8 ounces / 561 grams
  • Fill: 850+ down
  • Fill weight: 9.7 ounces / 274 grams
  • Warmth
  • Comfort: 39F
  • Limit: 30F
  • Extreme: NA
  • Packed dimensions: 2.6 liters
  • Materials: 15D Pertex
PROS

Exceptional warmth-to-weight ratio

Very light

Packs small

Generous neck baffle

Comfortable fit

Full-length zipper

CONS

Ok warmth, really a 40-degree bag

Stuff sack lacks compression straps

No stash pocket

Honorable Mention

A favorite among long-distance backpackers, this ultra-lightweight and exceptionally packable sleeping bag leverages high-tech materials and a narrow cut to keep weight at a minimum. The bag is warm and filled with 10 ounces of 850 fill down. The 10D ripstop nylon with DWR finish top fabric feels good to the skin. And we really appreciated the super smooth snag-proof light-weight zipper design with a full vertical hanging baffle to keep drafts from passing through. Mountain Hardwear also placed a one-inch strip of textured fabric along the zipper length to prevent snagging. The top of the bag has a cinchable four-chamber hood (not all ultralight bags do), a smallish draft collar, and a zipper garage to keep the nicely finished zipper pull from irritating your face. At the other end of the bag, the ergonomically designed footbox is comfortable and warm. The entire length of the bag is tuck-stitched and baffled to keep the down fill in place and minimize the potential for cold spots. Missing from this bag is a zippered pocket on the interior of the bag for small items like cell phones.

Burlier folks will want to try this bag before committing as the cut is narrow — a weight-saving trade-off. Some larger users complained they felt overly constrained. I did not. I’m 6-foot-3 and 215 pounds and felt a bit tight in the bag, but not uncomfortably so. It’s a performance mummy bag, dummy! Less material is less weight, and less volume is less air for your body to heat. I’d definitely pack it. Speaking of packing, this bag packs down incredibly small, about the size of two one-liter Nalgene bottles. It comes with a nice lightweight nylon compression sack and a large mesh storage sack. The Phantom is available in 30F, 15F, 0F, and 30F Alpine variants.

Product Specs
  • Weight: 22.3 ounces / 632 grams
  • Fill: 850 down
  • Fill weight: 10 ounces / 285 grams
  • Warmth
  • Comfort: 35F
  • Limit: 25F
  • Extreme: -5F
  • Packed dimensions: 4.1 liters
  • Materials: 10D recycled nylon ripstop shell
PROS

Extremely lightweight

Very high fill power down

Very compressible, packable

Snag proof zipper

CONS

Expensive

Tight cut

Best for Side Sleepers

I’ve used Sea to Summit’s dry bags for decades, and this was the first sleeping bag of theirs I have tested. The Spark is actually a series of similarly designed bags in 40F, 28F, 18F, and 5F options in both regular and long sizes. First, this bag is made from quality materials. The Spark series is made from 10D ripstop nylon on the shell and soft 7D nylon on the interior, which feels really good on the skin. In between is 850 power fill ultra-dry (hydrophobic) down that will help the down stay lofty in humid conditions.

So what do I like about this bag? I really appreciated some of the innovative design features of the Spark 28. For instance, this bag uses vertical baffles on the body and horizontal baffles on the legs and feet. This design will help keep side sleepers warmer because the vertical baffles on the body prevent the down from slipping down to the sides of the bag.

The ergonomic footbox also allows your feet to move at night without feeling constricted. It also has a nice zipper guard made from more rigid nylon to help prevent snagging. I’m 6-foot-3 and opted to test the men’s long version. I found it form-fitting but not uncomfortably snug. The Spark 28 also has a nice cinchable hood with a cinchable draft collar. Lastly, Sea to Summit has a wonderful lifetime warranty for this product.

What I don’t like about this bag? First, the baffles are sewn through instead of box baffles, which leads to more cold spots. (The 40F and 28F are sewn through and the 18F and 5F bags have box baffles.) Also, some users have reported they found the YKK #3 zipper is a bit finicky and hard to reach and unzip when inside the bag. I wish the draft tube along the zipper was a bit larger to provide more coverage, as well.
Also to note, the cinch for the hood and neck baffle are on the same paired drawstrings, which makes it a bit more difficult to adjust if you want a tighter hood and looser neck baffle or vice versa.

Product Specs
  • Weight: 17.3 ounces / 490 grams
  • Fill: 850+ down
  • Fill weight: 10.6 ounces / 300 grams
  • Warmth
  • Comfort: 35F
  • Limit: 28F
  • Extreme: NA
  • Packed dimensions: 2.5 liters
  • Materials: 10D recycled nylon ripstop shell, 7D liner
PROS

Very high warmth-to-weight ratio

Super light

Double zone full box baffle design

Packs down ridiculously small

Innovative vertical baffles on torso better for side sleepers

CONS

Less versatile half-length zipper

Sewn-through baffles

Smallish draft tube

Expensive

To be considered ultralight, a sleeping bag’s weight really should weigh in at 25 ounces or less. The Mountain Hardwear Bishop Pass 30 weighs 28 ounces, but I just couldn’t resist bringing it to your attention since it’s a great bag at a great price and pretty low weight. Sure, it’s not a 9.8-ounce Patagonia, but it’s also a lot warmer — so you won’t freeze your gonads off. The Bishop Pass 30 is Mountain Hardwear’s value bag. It doesn’t have the same high-tech features as the Phantom 30, but it’s solidly capable in its own right.

The Bishop Pass is a true 30-degree bag that is insulated with 12 ounces of 650 fill duck down and provides four inches of loft. The body fabric is made of 20D ripstop nylon with a DWR finish and it’s soft to the touch. Contributing to the bag’s weight is a more versatile full-length zipper that allows you to ventilate from both the torso and feet. Like the Phantom, it features a quality snag-proof YKK zipper pull, full-length hanging baffle, one-inch-wide anti-snag zipper lining, and a zipper pull garage near the collar for added comfort. The performance mummy cut is a bit roomier than the Phantom, but it’s efficient. The three-baffle hood is cinchable and features a down-filled face gasket around the collar. On the interior of the bag is a small Velcro-closed pocket to stow small items. The bag also has six hanging loops — two each at the foot, knee, and shoulder. The stuff sack is unremarkable and doesn’t have cinch straps, which makes the bag less packable than I’d prefer.

Just for fun, I stuffed the Bishop Pass into the Phantom’s stuff sack, cranked down the compression straps, and achieved nearly the same sized mass. Definitely invest in a compression stuff sack for this bag. This bag is a great value-buy, delivering true 30F warmth. It’s 6.3 ounces heavier than the Phantom and also $185 less, so you’re paying about $30 less per ounce than the Phantom and getting fairly similar warmth and greater durability. If cost is a concern, this is a great option.

Product Specs
  • Weight: 28.6 ounces / 810 grams
  • Fill: 650 down
  • Fill weight: 10.6 ounces / 300 grams
  • Warmth
  • Comfort: 40F
  • Limit: 30F
  • Extreme: -1F
  • Packed dimensions: 2.5 liters
  • Materials: 20D nylon ripstop
PROS

Affordable

Warm as rated

Packable, especially with compression stuff sack

Versatile ¾-length snag-proof zipper

Comfortable

CONS

Lacks neck baffle

Stuff sack lacks compression straps

Things to consider before buying an ultra-lightweight sleeping bag

Going fast and light in the backcountry means less strain and fatigue on your body and, typically, a more enjoyable time. Because ultra-lightweight sleeping bags tend to be expensive as hell, it’s important to really know what you need before you buy, and inevitably, you’ll be trading off some aspects of comfort, warmth, versatility, or a combination of all three to get a sleeping bag that weighs half as much as a normal backpacking sleeping bag. Ultra-lightweight bags shave ounces by using the highest-quality materials and the lightest and fluffiest down. Here are a few other things to think about.

Safety

I consider my sleeping bag and shelter to be more than just comfort items. They are essential parts of my survival system in the backcountry. Please make sure you know how to properly use ultra-lightweight gear before you err on the side of caution. Don’t let your urge to shave ounces put you in a situation where you might become hypothermic. Take the right gear for anticipated weather conditions, and also leave yourself a little bit of margin to boot.

Cut

Ultra-lightweight sleeping bags are most commonly designed in a form-fitting mummy bag shape. They are much more narrow at the foot, hips, and shoulders than regular sleeping bags to save weight on materials. They also typically have a hood with a neck or collar baffle that can be cinched tight around the nose and mouth to provide maximum warmth retention. Some UL bags don’t have a hood, so check before you decide. The advantage of a hood is that you’ll stay warmer. Bring a warm hat along if you decide to go hoodless, as most of the heat lost from your body in cold weather is through your head. (I don’t recommend hoodless bags.) The form-fitted cut of mummy bags may feel a bit more claustrophobic, but they also help keep you warm because there is less air for your body to heat on the interior of the bag.

Temperature rating

It’s critically important to understand sleeping bag warmth ratings. Frequently, manufacturers will market a bag at a lower temperature than its comfort rating. The good news is that every quality sleeping bag will have the comfort, lower limit, and extreme ratings printed on it somewhere — usually on the interior along the zipper. The comfort rating states the outside temperature at which a cold sleeper might still feel comfortable. The lower limit rating is the temperature at which a warm sleeper might still feel comfortable. The extreme rating is the lowest temperature a person could remain in the bag for six hours without risk of death from hypothermia.

Down insulation

Almost every UL sleeping bag is insulated with a high power fill goose down because it has the best warmth-to-weight ratio — far more than any synthetic fiber. The higher the number, the more lofty the down — and the higher the number, the better the down. For instance, a sleeping bag filled with 10 ounces of 800 fill down will provide the same warmth as a heavier, less packable bag filled with 20 ounces of 400 fill down. But, you gotta keep that down dry. When it gets wet, it clumps and loses its loft. No loft means no trapped warm air, which means a shivering you. So keep your down bag dry! To combat this, manufacturers have recently started using hydrophobic DWR finished down. The jury is out on how much hydrophobic down really helps. 

Packability

This is a measure of how small you can compress your sleeping bag. The smaller you can make it, the less room it takes in your pack, and the more you can get away with a smaller and lighter backpack. If your sleeping bag’s stuff sack doesn’t have compression straps on it, toss it and invest in a waterproof one that does. You’ll easily be able to reduce the size of the packed bag by half again with a compression sack. 

FAQs about ultralight sleeping bags

Q: How much should an ultralight sleeping bag weigh?

A: I consider any bag under 25 ounces to be an ultra-lightweight sleeping bag. 

Q: Is four pounds heavy for a sleeping bag?

A: Yes. Four pounds is a lot for a sleeping bag. If you’re car camping or just hiking a short distance, it might not matter much. Typically, bags weighing four pounds or more are roomier and more comfortable. If you’re going to be hiking long distances over multiple days, you’ll want the lightest bag you can afford. This is why I included the Mountain Hardwear Bishop Pass 30 as an option. At 28 ounces, it’s a lightweight bag, but not a UL bag, but it compresses about as small as a UL bag and costs hundreds less.

Q: Should I get a 15- or 30-degree ultralight sleeping bag?

A: It depends on how cold it will be where and when you are camping out. Typically, 30-degree bags are considered three-season (late spring, summer, and early fall) bags in most parts. If you are a cold sleeper, you might want a 20- or 15-degree bag. If you are looking to camp during the winter, you might opt for a four-season bag which might be a zero or negative-five-degree bag. 

Q: Is goose down good for UL sleeping bags?

A: Yes. Goose down is the preferred insulation for UL bags. Look for 800 power fill rated down or higher to get the most loft for the least weight. Note: It’s also the most expensive down.

Final thoughts

Are UL sleeping bags worth it? That’s a great question. If you hike long distances day after day, I think the weight savings is worth the cost. If you don’t, you can certainly get away with a bulkier, heavier, and maybe warmer bag. Just know that weight adds up, and when you’re backpacking, you gotta carry it all. Ultra-lightweight gear is all about tradeoffs — in this case, comfort, warmth, and/or versatility. The four most important (and heaviest) things you’ll carry backpacking are your pack, sleeping pad, shelter, and sleeping bag — so why not try to find the smallest and lightest (and least expensive) that minimally meet your long-distance backpacking needs?  

Methodology

I selected all of the ultra-lightweight sleeping bags in this review based on personal ownership, hands-on inspection, performance reputation, interviewing other experts, and thoroughly reviewing manufacturers’ specifications. I take my time to get to know the strengths and weaknesses of each item, and also check out the reviews of other experts just to make sure we’re not missing anything. For new items, I ask for samples from the makers and test them in the field. When that’s not possible, I visit the products in the store. In either case, I also review the manufacturers’ websites, user comments, YouTube reviews, and third-party evaluations, just to make sure I’m not missing anything.

When researching the best ultra-lightweight sleeping bags, I based my criteria on my own experiences using outdoor gear in the field for more than 35 years. I’m very familiar with the major manufacturers of outdoor equipment, know their reputations, and have a sense of their customer service — which is also super important. I also speak with other people who spend considerable time outdoors for their thoughts as well. 

After gathering enough high-performing products for a best-of article, I racked and stacked each based on their attributes, design, and performance. My bias is towards the lightest, best-functioning, and lowest-cost solutions available. We don’t torture test gear here at Task & Purpose — we test within normal usage limits. When gear does fail or break, we contact the manufacturer to see if and how it stands by its products. I also take a look at how easy the gear is to maintain or repair in the field — the simpler, the better.

For final selection, I take all factors into consideration and think: What is the gear I’d most want in my pack? What would I trust my life to in the backcountry? Those are the recommendations I forward for your consideration. Furthermore, it’s of the utmost importance to the Task & Purpose team that our readers know our commitment to open, fair product recommendations and reviews, and that you can trust us to provide you with unbiased, balanced information.

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