Western Mountaineering UltraLite 20°F Sleeping Bag

Twenty Degrees. Under Two Pounds. No Unnecessary Fuss.

The Western Mountaineering UltraLite is a remarkably accomplished three-season sleeping bag for backpackers who appreciate the finer points of traveling light without making unnecessary sacrifices in comfort. Filled with premium 850+ fill power goose down and wrapped in an exceptionally lightweight shell, it delivers an impressive amount of warmth for its modest weight.

At just 1 pound, 13 ounces in the 6'0" size, it's the sort of sleeping bag that makes you reconsider how much equipment you really need to carry. Whether you're working your way along the John Muir Trail, spending a few nights above treeline in Colorado, or simply looking for a dependable companion for a long season of backpacking, the UltraLite makes a compelling case for itself.

And it does so without making a fuss about it.

Western Mountaineering UltraLite Specs

Additional specifications

Sizes and zipper sides in stock vary. Pick yours in the options above, and call or message the store if you do not see the one you need.

Who the UltraLite Is For

• Thru-hikers and weekend backpackers who want one bag for spring, summer, and fall trips, including nights when temperatures may approach the 20°F rating.

• Weight-counters who would rather carry less and adjust their clothing or sleep system than carry a heavier bag.

• Anyone shrinking their pack. At 7" x 13", the UltraLite takes up remarkably little room.

Who Should Look at Something Else

• Cold sleepers or high-elevation campers. If you tend to sleep cold, consider choosing a bag rated 5–10°F colder than the lowest temperature you expect. The 10°F VersaLite is worth a look.

• Side sleepers and restless sleepers. The UltraLite has a traditional, relatively trim mummy cut. If you want more room while keeping a mummy-bag design, consider the AlpinLite 20°F. If you prefer a much roomier design that opens flat like a quilt, look at the 35°F DreamLite.

• Warm-weather travelers. The 32°F SummerLite and 35°F HighLite are lighter options for trips when the extra insulation isn't necessary.

• Mostly car campers. You may not get much practical benefit from paying for the UltraLite's considerable weight savings if you're not carrying it very far.

What Makes It Warm and Light

• 850+ fill power goose down. High fill power means more loft for the weight, so the bag provides excellent insulation without becoming heavy. Western Mountaineering says its down is ethically sourced.

• Insulated draft tube. A down-filled tube runs along the zipper to block cold air where sleeping bags can otherwise lose heat.

• Full insulated collar and cinching hood. The collar helps seal warmth around your shoulders, while the hood pulls snug when the temperature drops.

• Continuous baffles. The down isn't locked into sewn chambers, so you can shift it toward the top for additional insulation on colder nights.

• 12-denier ripstop nylon shell. Lightweight and tightly woven, the shell helps resist incidental moisture while allowing body moisture vapor to escape.

• Full-length #5 YKK zipper. A lightweight zipper that runs smoothly and allows convenient entry and ventilation.

How to Choose Your Size

The UltraLite is a mummy bag, so the cut is snug on purpose. A closer-fitting bag has less empty space for your body to heat, which helps make the most of its insulation.

But snug should not mean uncomfortable.

Check the girth measurements in the table above. In the 6'0" length, the UltraLite measures 59" at the shoulders, 51" at the hips, and 38" at the foot. These measurements describe the circumference of the bag's interior—not your body measurements.

If you are between lengths, have broader shoulders or hips, sleep with several layers, or like room to roll over, take a closer look at the girth numbers before ordering. The AlpinLite offers additional room through the shoulders and hips while retaining a traditional mummy shape.

And if you're uncertain, ask us. We'd rather help you choose the right bag than have you discover the fit isn't quite right halfway through a trip.

UltraLite vs. Other Western Mountaineering Bags (6'0" Size)

The UltraLite sits in a particularly useful spot in the lineup. Compared with the HighLite, it weighs about 13 ounces more but offers a 15°F lower temperature rating. Compared with the VersaLite, it saves about 3 ounces while giving up 10°F of temperature rating.

The AlpinLite is perhaps the most interesting comparison: it has the same 20°F rating but adds meaningful room through the shoulders and hips. That extra space is worth the small weight increase if a traditional mummy bag feels too restrictive.

If you're on the fence, ask us. We're happy to help sort through the differences.

What to Pair It With

• A properly insulated sleeping pad. Your sleeping pad is an important part of your sleep system. For colder conditions, an R-value around 5 or higher is a sensible target. See our sleeping pads.

• A pillow and a liner. Both can add comfort and help keep your bag cleaner between washes. See our pillows.

• A pack with room to spare. The UltraLite's compact packed size makes it easier to keep your backpack streamlined. Browse our backpacking packs.

UltraLite Questions

What temperature is the UltraLite rated for?

The UltraLite is rated to 20°F (-7°C). Western Mountaineering describes its temperature ratings as guidelines for comparing sleeping bags, not guarantees of individual comfort. Its rating generally falls between the limit and comfort figures used in standard EN/ISO testing. If you sleep cold, Western Mountaineering suggests choosing a bag rated 5–10°F colder than the lowest temperature you expect to encounter.

Is the UltraLite a winter sleeping bag?

No. The UltraLite is primarily a three-season sleeping bag. It is a versatile choice for spring, summer, and fall backpacking, but for regular nights well below 20°F, consider a colder-rated bag such as the 10°F VersaLite. Western Mountaineering also offers an overfill option that adds roughly 5°F of warmth, available as a custom order.

How much does the UltraLite weigh and how small does it pack?

In the 6'0" size, the UltraLite weighs 1 lb 13 oz (820 g) and packs to approximately 7" x 13". The 5'6" version weighs 1 lb 12 oz, and the 6'6" version weighs 1 lb 15 oz. All three lengths have the same listed stuff size.

What size should I buy?

Western Mountaineering makes the UltraLite in 5'6", 6'0", and 6'6" lengths. Choose a length based on your height, then check the interior girth measurements to make sure the bag offers enough room through your shoulders, hips, and feet. A mummy bag is designed to fit closely. If you want more room without giving up the mummy shape, consider the AlpinLite.

What sleeping pad should I use with the UltraLite?

Your sleeping pad plays a major role in keeping you warm. Western Mountaineering's temperature-rating guidance assumes an insulated ground pad. For colder conditions, an R-value around 5 or higher is a sensible target; for milder summer and shoulder-season trips, an R-value around 3–5 may be appropriate depending on conditions.

Is the UltraLite waterproof?

No. Its 12-denier ripstop shell is tightly woven and helps resist incidental moisture while allowing body moisture vapor to escape, but it is not waterproof. Like any down sleeping bag, the UltraLite performs best when kept dry. Protect it inside a dry bag or pack liner while traveling.

How do I wash and store the UltraLite?

Western Mountaineering suggests laundering the bag after a season of regular use. Follow the manufacturer's care instructions and use a suitable down wash. Dry it carefully on low heat, using clean tennis balls or dryer balls to help restore the loft. Store it loose in the included breathable storage bag—not compressed in its stuff sack—in a cool, dry place away from sunlight.

Does the UltraLite have a warranty?

Yes. Western Mountaineering covers manufacturer defects for the life of the bag. Normal wear and misuse are not covered. A broken stitch may be covered, for example, while a tear caused by field damage is not. Many repairs, including tears and zipper problems, can be handled at the company's factory in San Jose, California.

Where is the UltraLite made?

The UltraLite is made in the USA by Western Mountaineering.

Why Buy from Quest Outdoors?

Quest has been an outdoor gear store in Louisville, Kentucky, since 1984. You can talk with people who know the gear and can help you choose the right equipment for your adventures. Western Mountaineering sleeping bags ship free by ground.