Alpine Down Winter Sleeping Bag (-5°F & -40°F)
Shipping & Returns
Our warehouse is actively shipping orders from 8am to 1pm MST Monday through Friday. Most orders ship in one business day, but the transit time can take up to 7 days, depending on your distance from Boulder, Colorado.
2nd Day and Next Day Air orders will ship same day if placed by 1pm MST, Monday-Friday (except holidays).
All orders are eligible for fast and easy returns within 60 days of purchase.
For more details, please check out our Help Center
The EN Rating scale is a scientific test to determine the warmth of a sleeping bag. The test produces a Lower rating (for male sleepers) and a Comfort rating (for female sleepers). Both are listed in the features table on the product page.
A unisex sleeping bag with a Lower limit of 14ºF means a man should be comfortable down to air temperatures of 14ºF. The same bag will also have a Comfort limit, in the realm of 27°F, so a woman would be comfortable down to an air temperature of 27ºF. These ratings require a sleeping mat with an R-Value appropriate for expected ground temperatures – without this, the sleeping bag itself is unlikely to keep the sleeper warm enough.
A variety of factors impact sleeping bag warmth - the above temperatures are merely guidelines, not guarantees. It’s important to think of a sleeping bag, an appropriately insulating sleeping pad and a liner as a sleep system. For example - if you plan on sleeping in nighttime air temperatures of 27ºF / -3°C, choose a bag with a gender-appropriate rating of 23°F / -5°C, plus a sleeping mat with an R-Value of 2.5 to 3, and consider a Reactor thermal liner.
The Alpine down mummy sleeping bag is designed for the rarefied world of high-altitude and arctic conditions. It features cutting-edge materials, the highest quality Ultra-Dry down, and complex construction. Expedition mummy sizing allows you to wear extra clothing, and boot liners inside the bag.
If you are going above or beyond, the Alpine is the bag you will want to take with you.
Nano Shell™ is a 20 Denier Nylon fabric with a water-shedding DWR finish on the exterior and a microporous PU coating on the interior. This highly breathable, highly water-resistant, windproof shell fabric is used on the Sea to Summit Alpine sleeping bags and Cinder quilts where it protects the down from external moisture even during very wet conditions.
The highest-lofting down used in any of Sea to Summit’s sleeping bags. 850+ Fill Power indicates that one ounce (30g) of down will re-expand to over 850 cubic inches after compression. Higher loft means that less down can be used to achieve the same temperature rating – important for performance sleeping bags. The loft and down quality/composition are independently tested by the International Down and Feather Laboratory (IDFL) – a copy of the certification is supplied with every Sea to Summit sleeping bag. The down is responsibly sourced and RDS certified and treated with the environmentally-friendly Ultra-Dry Down™ treatment.
100% of the down used in our sleeping bags and quilts is independently certified to the Responsible Down Standard (RDS). The RDS certifies down against animal welfare requirements and tracks it from the source to the final product. The purchase of RDS certified products demonstrates demand for better animal welfare practices in the down and feather supply chain. Sea to Summit is certified to the RDS. To learn more about RDS visit https://textileexchange.org/standards/responsible-down/
Our Free-Flow triple-zip design ensures your sleeping bag retains maximum warmth and efficiency when needed and multiple ventilation options when it's not. The half-zip on the right side of the bag (left side on women's bags) provides freedom of movement for both arms, additional ventilation and allows the top third of the bag to be folded down as a mini quilt when the mercury climbs higher than expected.
Comes WithUltra-Sil Compression Sack & Storage Cube
InsulationUltra-Dry Down 850+ Loft
Shell FabricWater repellent NanoShell
Zip OptionsFree-Flow zipper system
|-5°F Regular||-5°F Long||-40°F Regular||-40°F Long|
Frequently Asked questions
Is this sleeping bag warm enough for cold-weather use?
Yes, this is a great sleeping bag for cold-weather camping. The Alpine -40° bag features a high-lofting down, technical hood, oversized draft tubs, and draft collar to keep you warm on the coldest nights. And, Alpine -5°F is designed for the extreme cold of alpine expedition use. We recommend Ascent/Altitude or ultralight Spark/Flame sleeping bags for occasional cold-weather use..
Can this sleeping bag be used in bivvies?
Yes! This sleeping bag features a NanoShell shell fabric that's windproof and highly water-resistant to protect the Ultra-Dry Down from external moisture.
Can this sleeping bag be zipped to another sleeping bag?
Unfortunately, the Alpine sleeping bag is not designed to be joined with another bag.