If you are planning an outing this winter that is likely to include an outdoor sleepover, staying warm is bound to become your number one priority. A decent sleeping bag is key when it comes to avoiding hypothermia in colder months, but how do you pick the best 40 degree backpacking sleeping bag for your outing? This question is answered below in the Shopping Guide section, following our selection of reliable and comfortable cold-weather sleeping bags for the most extreme conditions where each product stands out in a certain category that it represents.
I can recommend the Marmot CWM 40 below sleeping bag as my absolute favorite among cold-friendly models for those who are short of time. Since it is far from what you might refer to as budget-friendly, though, I have also included a number of considerably more affordable products that still deliver, plus a premium option for those willing to invest in their winter-time comfort.
Top 6 Minus 40 Sleeping Bag Models, Reviewed
- MARMOT CWM
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- FUNDANGO Cold All Weather Lightweight Compact Backpacking 40 Degree Sleeping Bag
- Envelope Sleeping Bag
- High Peak Outdoors Cascade -40-Degree Sleeping Bag
- ATEPA Lightweight Compact Backpacking Sleeping Bag
In this section, I’m sharing my impressions of some of the best 40 degree sleeping bag shopping options out there and why this or that product can be a viable solution.
1. Marmot CWM: Best 40 Below Zero Sleeping Bag Overall
Made by a US-based brand with a nearly 50 years’ history, this sleeping bag is packed with features to keep you warm on a really cold night.
It uses the mummy-like shape, which is generally the warmest option. One of the key downsides of this design is that it falls on the restrictive side. Marmot tried to overcome this difficulty by providing as much inner space as reasonably possible.
The model is filled with 800-fill down for maximum warmth. On the outside, it bears a double-layer Pertex Shield installation, a proprietary synthetic fabric that is both breathable and waterproof, below which lies a lining of 30D nylon Pertex Microlight. It is more likely than not to feel too hot unless the weather is really brutal, but it stays blissfully dry and warm under the most brutal conditions.
The sleeping bag comes in two sizes, 72 and 78 inches long. There are two zip positioning options (right or left) to choose from for each size. The bafflings are designed in a way that makes the bag stretchable as you move and not prone to clumping. Additionally, the reinforced foot area along with well-made zippers mean that it is likely to become an investment to last. Speaking of investment, though, it is pricey.
- Extremely warm;
- Ample foot space as for a mummy design;
- Built to last;
- Water- and windproof;
- Clump-free baffling design.
- On the lofty side;
2. Western Mountaineering Bison LZ Gore WindStopper: An Ultralight 40 Degree Sleeping Bag
A product of another American company that has been in the business for nearly half a century, this sleeping bag is meant to keep you safe in extreme cold without being too bulky.
Stuffed with 42 oz. of 850 fill power down, it boasts a total weight of just 4 lbs. 10 oz. Combined with the traditional mummy design that features a warming hood ruff, it makes it one of the best cold-weather options for winter-time mountaineering.
In terms of design, this sleeping bag is reasonably lofty at 10 inches for efficient heat distribution. The V-block side baffle works well to provide more space for movement inside the bag. This is paired with a set of horizontal baffles that prevent down displacement.
On the outside, there is Gore’s proprietary Windstopper fabric, which is similar to the iconic Gore-Tex except it does not have the waterproofing capabilities of the latter. If you are planning a hiking tour somewhere windy, though, this sleeping bag can be a great choice. Just like the top pick, you should expect it to feel warmer than desirable on not-so-cold days. The product only comes in one size, labeled 6’0″, with two zipper options.
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- Highly windproof;
- Very warm;
- The baffle design helps the down stay in place;
- Reasonable price.
- Not for claustrophobic people;
- Not waterproof.
3. FUNDANGO 3-in-1 Warm & Cool Weather Sleeping Bag: An Affordable and Versatile 40 Degree Down Sleeping Bag
Suppose you aren’t sure whether you are going to face bitter cold during the next outing. In that case, this Fundango bag might be the optimum solution as it combines considerable warming potential with breathability for warmer weather.
Please be aware that, even though I have included this model in my 40 degree sleeping bag review section, it is not officially rated for extreme cold. Its lowest point, according to the label, is 10.4 degrees Fahrenheit. However, the combination of 300GSM hollow fiber and a waterproof 190T polyester lining makes it warm enough for most occasions during the cold season.
You should consider this model if mummy-style bags feel too tight around your body — there is a lot of space in this comfortable, skin-friendly 75″ x 30″ envelope. It is lightweight, too, at just 3.2 pounds. Another advantage of the envelope-like design is that you can zip two bags together on a warmer day and get a double bag.
- 【All Weather Sleeping Bag】The dimensions of the adult sleeping bag is (75 x 30 Inches). Fits most people up to 6 feet tallComfort temperature range of the portable sleeping bag is 35.6°F/2℃ to 44.6°F/7℃.Extreme use down to 10.4°F/-12℃. Filled with 300GSM hollow fiber with 100% polyester lining and 100% polyester filling which make it softness and warmth great for outdoor sleepovers.You can use the 4 season sleeping bag form spring, summer, fall to early winter.
- Wide temperature range;
- Roomy lightweight design;
- Transforms into a boudle bag easily;
- Not as warm as dedicated cold-weather mummy bags.
4. SOULOUT: A 4-Season Sleeping Bag 40 Degree Friendly Version
Another item on the list is not really rated for 40 degrees below zero. This all-season bag does deserve to be included because it is filled with 400 GSM synthetic fiber and boasts a soft lining of brushed flannel for optimum warmth and comfort.
The exterior bears a 290T polyester lining for added water resistance, designed in a way to prevent condensation and humidity in general, which is a common problem with budget-friendly sleeping bags. With a weight of 6.97 pounds, I wouldn’t call the model especially lightweight, but it is reasonably portable.
This model comes in two options, single and double, the former measuring 59” W x 87” H (this means it is long enough for people up to 6.5’ tall.
- COMFORTABLE, DURABLE, SKIN FRIENDLY– 100% polyester lining is skin-friendly & comfortable. High quality 290T polyester makes it durability. You will be comfortable no matter how hard and rough the ground is.
- Affordable price;
- Suitable for all seasons;
- The roomy design keeps the heat in;
- Soft to the touch.
- On the heavy side;
- Not the warmest option.
5. High Peak Outdoors Cascade: A Great Minus 40 Sleeping Bag for Couples
Designed by a German-based company with over 35 years of experience, this mummy-style cold-weather sleeping bag stands out in its class because it can be zipped together with another piece to form an ultra-warm abode for two.
Underneath the water-resistant Nylon Taffeta shell, there is dense yet stretch Invista Tactel fiber filling to keep you warm in your sleep. It comes with a hood and a drawstring closure and measures 86 inches long and 34 inches wide, making it a great option if you are taller than average or simply like to have a lot of space around your feet (the foot area is 22 inches wide). Unfortunately, the product is relatively heavy at 8 pounds, but it comes with an easy-to-use compression bag to make it more compact. Only one design and color option are available.
- Very warm;
- Not likely to get wet;
- Not prone to condensation;
- Can be zipped together with another bag.
- Not completely waterproof;
- Only one size and zipper option.
6. ATEPA Mummy Bag: A Lightweight 40 Degree Sleeping Bag on a Budget
Officially rated for 32°F to 50°F, this sleeping bag combines the warm mummy design with a weight as light as 2.4 pounds. It measures 84.6 inches long but folds easily to just 13.8 × 6.7 inches, partly at the cost of not-so-generous foot space and partly due to the compression sack that comes with it.
The outer layer is made of tear-resistant and waterproof 210T polyester, beneath which lies 230T polyester for extra warmth. While being effective and keeping the heat in, the model is prone to some condensation.
Special attention has been paid to making the bag ergonomic, with a bunch of useful features such as a torch pocket. Two zipper options are available. You can also zip two pieces together and get a double sleeping bag.
- ★★【Give You 3-Season Warmth】The comfort temperature range of the backpacking sleeping bag is 32°F to 50°F.Extreme use down to 32°F.You can use the sleeping bag form late spring to early fall. Ideal for outdoor camping trips,trekking,boy scouts or mountain hiking.
- Zip-together feature;
- Reasonably warm;
- Less foot space than ideal.
Shopping Guide: Picking The Best -40 Degree Sleeping Bag
Choosing a sleeping bag, you can rely on in winter can be a challenging task given how similar yet diverse products in this category appear to be. Here’s a quick guide to help you make a decision you won’t regret.
Types of sleeping bags
Sleeping bags come in three basic shapes. These are mummy, envelope (rectangular), and semi-rectangular. Mummy-style bags look like a wrap around your body, which means maximum warmth and, unfortunately, maximum restriction. At the other end of the spectrum is the rectangular design that gives you a lot of room but is less efficient in terms of preserving heat, while the semi-rectangular option combines features of both of the above.
Another aspect to take into account is the air temperature rating, described by the upper and lower limits and the comfort temperature. This translates to descriptive terms such as summer, winter, or three-season (spring to fall).
The technology behind this classification is primarily the insulation, represented by two common categories — down and synthetic (usually specialized polyester). The key tradeoff here is weight vs. warmth. Synthetic-insulated bags tend to be bulkier, but they also cost less. With down, you can get as warm as you wish without having to carry a heavy load, which is naturally reflected by the price.
Do I need a -40 degree backpacking sleeping bag?
What makes sleeping bags 40 degrees bags is their ability to keep you alive and, ideally, comfortable at a temperature of 40 degrees Fahrenheit below zero. This is about the warmest sleeping bag you can get. Apart from having a lot of effective insulation, it needs a wind-proof and water-resistant shell to protect you from the elements.
Most models rated for such extreme temperatures are classified as winter sleeping bags and are almost sure to be too hot for warmer conditions. Therefore, I recommend investing in a 40 below sleeping bag only if you are planning to engage in winter outings in extra-cold locations such as certain mountainous areas.
In the list above, you’ll find some models that don’t officially promise protection at -40 or lower. Yet, they are reasonably warm for most settings without being too much of an oven in less extreme weather.
What to look for when buying a -40 degree backpacking sleeping bag
The first thing to make up your mind about is the shape. Avoid mummy designs if you are heavily claustrophobic, opting for semi-rectangular or envelope options instead.
Next, consider the materials. Down is generally preferable; the higher the fill power number, the warmer it is likely to be. Synthetic fabrics like polyester can ensure sufficient protection as well, though, especially when combined with a water- and wind-proof outer lining.
Make sure you get the right size depending on your body type, preferably with the zipper opposite to your dominant hand. If you like to connect your bag with someone else’s, consider getting one with a zip-together feature (this one is more common in envelope-style bags). Finally, like most hiking gear, a good sleeping bag should be lightweight and compact.
Stay Snug and Warm with the Right Sleeping Bag
If you are planning a winter-time mountaineering trip, a quality 40 below sleeping bag is key to your comfort, if not survival. A mummy-shaped model generously filled with high fill power natural down, such as the Marmot CWM, will keep you warm throughout the night and provide the necessary protection.
Those looking for more versatile options, though, might be interested in synthetic-insulation sleeping bags that give you more space around your body while fighting off cold and wind. Whatever option you choose, be sure to keep balance between portability and warmth, and remember that the latter is likely to be vital under extreme conditions.
For the purpose of statistics, I encourage you to share your winter trip plans in the Comments section below. What is that cold place you are going to? Share the destination of your dreams with fellow hiking enthusiasts, and don’t forget to stay warm!