Feathered Friends Swallow UL20 Sleeping Bag Review

Bottom Line

The Feathered Friends Swallow UL20 stands out for its exceptional warmth-to-weight ratio, premium materials, and thru-hiker tested craftsmanship. On our 30-mile backpacking trip through Colorado’s Maroon Bells-Snowmass Wilderness, it proved impressively warm, living up to its 20°F claim. The 950+ fill power goose down outperforms most other sleeping bags we tested as a super lofty, efficient, and ultralight insulator. It’s also incredibly compressible, saving valuable space in your pack. 

Its comfort is on par with most mummy bags, though broad-shouldered or restless sleepers may find it slightly snug. We also wish it included a small interior pocket, but its minimalist design keeps the weight impressively low.

This is a bag for dedicated backpackers who prioritize warmth, packability, and long-term value. The price point represents an investment in weight savings and quality sleep rather than a budget bag to serve a casual annual trip.

HOW WE TESTED

Through decades of hands-on experience in the backcountry, we’ve assessed dozens of sleeping bags in every condition imaginable. We took the Swallow UL20 on a 30-mile backpacking trip in the Maroon Bells-Snowmass Wilderness of Colorado during a chilly Rocky Mountain Autumn. We used our years of knowledge to assess the bag’s warmth, comfort, weight, packability, and features.

Warmth

We were seriously impressed with the Feathered Friends Swallow UL20’s warmth, even when pushed to its limits. Even though Feathered Friends doesn’t list an EN or ISO comfort rating, we think the Swallow UL20 comes very close to its 20°F claim – a rarity in the sleeping bag world.

On a chilly trip through Colorado’s Elk Range, this bag kept us toasty warm all night long with nighttime temps into the low 30s. The regular size, 20-degree version packs 16.8 ounces of exceptional 950+ fill power goose down insulation. The incredibly high fill power helps the down keep your body heat trapped inside. The horizontal baffles help keep the down evenly distributed, minimizing cold spots and preventing heat from escaping through thin areas.

The mummy shape also plays a key role, minimizing dead space so your body heat warms the interior faster.

The Swallow comes in both 20°F and 30°F versions, and we’d consider both solid three-season options. Go with the 20°F if you tend to run cold, or the 30°F if you’re a naturally warm sleeper looking to save a few ounces.

Comfort

Feathered Friends nailed the balance of comfort and warmth with the Swallow UL20. Mummy bags are inherently more thermally efficient than rectangular bags or quilts, but they often feel tight or even claustrophobic. The Swallow strikes a happy middle ground. It’s not sprawling by any means, but it offers average to slightly above-average roominess for its class.

The footbox is the most tapered area at 42 inches in circumference, helping to keep your feet snug and warm. For most sleepers, that’s ideal, but if you tend to thrash or “karate kick” in your sleep, you might find it a touch restrictive.

The bag tapers from 55 inches at the hips to 64 inches at the elbows, providing enough room for most guys and gals to move around without losing much heat. The shoulder girth measures 60 inches, which is roomy enough in our experience, but might be a bit constricting for stockier guys. The hood is pleasantly roomy and large enough to secure a small pillow.

For fall 2025, Feathered Friends gave the Swallow a notable upgrade with a Pertex Quantum Pro shell and Pertex Diamond Fuse fabric reinforcing the footbox. The result is a fabric that feels both softer and more durable than most ultralight materials – adding a touch of luxury to an otherwise performance-focused design.

Weight & Packability

The Feathered Friends Swallow UL20 is one of the lightest true sleeping bags on the market — and it does so without cutting corners on warmth or creating dishonest claims. At just 1 pound 11.3 ounces for the regular length (without its stuff sack), the UL20 is impressively light for a 20-degree bag. The long version adds a mere 1.4 ounces. Or, if you want to go as light as possible, the UL30 can get as low as 1 pound 8.3 ounces. 

That ultra-high fill power down also means outstanding compressibility. Whether you are utilizing the included stuff sack or just free packing around the empty space in your bag, the UL20 takes up minimal real estate.

Features

The Swallow UL20 keeps things refreshingly simple (and lightweight) by including only the essentials. You won’t find any gimmicks here, just well-executed features that serve a clear purpose. The standard plastic zipper glides smoothly along without excessive snagging, even when you’re half-asleep and fumbling in the dark. A roomy hood cinches down snugly with a drawcord to seal in warmth, and a small draft collar with a snap closure helps block out stray drafts at the top – though we found the snap itself doesn’t add much functionally.

Feathered Friends clearly prioritized weight savings over extras, skipping things like interior pockets, glow-in-the-dark zipper pulls, or arm openings that can add bulk and weight. Still, we wouldn’t mind a small internal stash pocket for keeping a phone or water filter warm on frigid nights.

Overall, the pared-down feature set perfectly aligns with the Swallow UL20’s ultralight philosophy. It gives you everything you need and nothing you don’t, maintaining the focus on warmth, quality, and weight savings.

Should You Buy the Feathered Friends Swallow UL20?

The Feathered Friends Swallow UL20 is built for serious backpackers and thru-hikers who want maximum warmth from the lightest possible package. It’s ideal for those who count ounces but still expect reliable comfort in below-freezing conditions. The combination of 950+ fill power down, efficient design, and premium materials make it one of our favorite sleeping bags of all time.

The Swallow UL20 isn’t designed for casual campers or those who like roomy comfort and extra features. Its minimalist design and mummy shape may feel restrictive to those who desire extra luxury. 

Though it’s certainly not a budget bag, the Swallow’s exceptional warmth-to-weight ratio, durability, and craftsmanship deliver a lot of value for serious adventurers. For those who spend countless nights in the backcountry, it’s a long-term investment in warmth and quality sleep.

What Other Backpacking Sleeping Bags Should You Consider?

For more options, see our full guide to the best sleeping bags for backpackers, including these bags:

REI Magma 15 Review: If you’re looking for similar warmth as the UL20 at a more affordable price, the Magma 15 can deliver. It’s noticeably heavier than the UL20 but also one of the most accurately rated bags we’ve tested. We’ve used the Magma time and time again in cold conditions and were consistently impressed with its thermal efficiency.

Western Mountaineering UltraLite 20 Review: When it comes to top-of-the-line bags made by cottage companies with an eye towards quality, the Western Mountaineering UltraLite 20 is directly competitive by price, fill power, and warmth. The UltraLite 20, however, is lighter, has a higher temperature rating, and offers a wider cut, making it more comfortable and versatile for more users.

Feathered Friends Swallow YF 20 Review: For a slightly heavier and warmer version of this bag, try the Feathered Friends Swallow YF 20 – which uses a more durable, 20D YFuse fabric.