The Best Sub zero Sleeping Bag for Extreme Cold: Expert Review!


As an avid winter camper, you know the importance of staying warm in extreme cold. Your sleeping bag is one of the most critical pieces of gear to consider for subzero temperatures. With so many options on the market touting various temperature ratings and features, determining the best sub zero sleeping bag for your needs can be challenging.

This article provides an expert review of the top sub zero sleeping bag currently available based on warmth, weight, packed size, and cost. Whether you are planning an expedition to the Arctic or just want the assurance of a bag that will keep you toasty on the coldest of nights, this guide will help you find a sleeping bag you can rely on in extreme cold. With the right bag, you can adventure out in the depths of winter confident you will sleep soundly through the night.

Sub zero Sleeping Bag

Sub zero Sleeping Bag

The Best Sub zero Sleeping Bag for Extreme Cold: Expert Review!

What Temperature Rating Do I Need for a Sub zero Sleeping Bag?

To determine the appropriate temperature rating for a sub zero sleeping bag, you must first consider how cold the environment will be where you plan to use it. The rating indicates the lowest temperature at which a typical user should remain comfortable, but it does not indicate the extreme low temperature limit.

For most subzero conditions, a rating between -10 to -20 degrees Fahrenheit (-23 to -29 degrees Celsius) should suit the needs of an average sleeper. However, for extreme cold weather camping or mountaineering, a rating of at least -30 degrees Fahrenheit (-34 degrees Celsius) or lower is recommended. Some bags are rated as low as -60 degrees Fahrenheit (-51 degrees Celsius) for polar conditions.

Additional factors to consider when determining the temperature rating you need include:

  1. Your own tolerance for cold. If you tend to feel cold easily, choose a lower rating.
  2. The insulation type and fill power. Higher fill power down and synthetic insulations provide better insulation for their weight.
  3. Added insulation layers. Having a sleeping pad, liner, bivy sack, and wearing insulated clothing inside the bag can increase the overall temperature rating by up to 15-20 degrees Fahrenheit.
  4. Your activity level. More active days require warmer bags since your body will have less ability to stay warm at night. Less active days may require slightly lower ratings.

By considering these factors and determining the coldest temperatures you are likely to experience, you can choose a subzero sleeping bag with an appropriate EN lower limit rating to keep you safe and comfortable in extreme cold weather conditions. The investment in a high-quality bag can be lifesaving.

Fill Power: How Much Insulation Do You Need?

Sub zero Sleeping Bag

Sub zero Sleeping Bag

To determine how much insulation you need in a sub zero sleeping bag, consider the fill power and temperature rating.

Fill power refers to the amount of insulation stuffed into the bag, measured in cubic inches per ounce. The higher the fill power, the more air pockets are trapped, providing better insulation. For extreme cold, choose 800 fill power or higher.

  • 800-850 fill power is suitable for most subzero conditions. It provides excellent insulation for its weight.
  • 900 fill power or higher is ideal for extreme subzero temperatures below -20°F. It packs the most insulation into the lightest bag.

Next, check the temperature rating, which indicates the lowest temperature the bag is designed to keep the average sleeper warm. For extreme cold, choose a rating of at least -20°F or lower.

  • -20°F to -40°F is suitable for most winter camping and mountaineering.
  • -45°F or lower is necessary for expeditions in extreme polar conditions.

To determine which rating you need, consider factors like if you sleep warm or cold, use of a sleeping pad, shelter, and clothing. It is best to overestimate the rating to ensure you stay warm.

With the right combination of fill power and temperature rating for the conditions, a high-quality sub zero sleeping bag can keep you safe and comfortable in the most frigid environments. Choosing a bag specifically designed for extreme cold will help ensure you get a good night’s rest even when the temperatures plummet.

Shell Material: Why Down Fill Isn’t Enough

Shell Material

For sub zero sleeping bags, the shell material is just as important as the fill. A high-quality, water-resistant shell is necessary to protect the down fill from getting wet since down loses much of its insulating ability when damp. The shell also helps block wind and weather, keeping the fill in place.

The best sub zero sleeping bag shells are made of tightly woven, ripstop nylon with a water-resistant coating, such as polyurethane. Ripstop nylon is lightweight but durable, resisting tears and damage. A higher denier, such as 40D to 70D, will be more durable while still allowing some breathability. Water-resistant coatings provide protection from moisture while still remaining breathable. Some high-end bags may use waterproof membranes like Gore-Tex for the ultimate in weather protection.

For extreme cold, a double shell construction is ideal. An inner shell holds the fill in place, while an outer shell provides maximum weather resistance. Multiple baffles, or chambers of fill, between the shells also help insulate. The more baffles, the less cold air can penetrate and the better the bag retains heat.

Other considerations for shell material include:

  • Seam sealing: Seams and zippers are common areas for air and water penetration. Sealed or taped seams prevent leakage and drafts.
  • Zipper coverage: A zipper garage or draft tube covers the zipper to block air flow. An insulated zipper flap provides even more coverage.
  • Hood: An insulated hood that cinches tightly around your face helps contain body heat. Look for a hood with multiple baffles and adjustment points.
  • Pockets: Interior pockets allow you to keep electronics, maps and other items warm and accessible. Exterior pockets may not be well-insulated.

For extreme cold weather camping, a high-quality sleeping bag shell is just as important as the fill for comfort and safety. Choose a ripstop nylon shell with a water-resistant coating and double construction for the best protection from the elements. Sealed seams, zipper coverage, an insulated hood, and interior pockets will ensure you stay warm in the coldest conditions.

Sleeping Bag Shape: Mummy vs. Rectangular for Subzero Camping

When choosing a sleeping bag for subzero camping, the shape is an important factor to consider for warmth and comfort. The two most common options are mummy and rectangular bags.

Mummy Sleeping Bags

Mummy sleeping bags are tapered at the feet, narrow at the shoulders, and close-fitting, which helps maximize insulation for the minimal amount of space. The tight fit also reduces dead air space to keep you warmer. Mummy bags are ideal for ultralight backpacking and mountaineering where pack space and weight are limited. However, the narrow cut can feel confining for some.

Rectangular Sleeping Bags

Rectangular sleeping bags have a more spacious design, as the name suggests. They have a boxier cut with extra room at the shoulders and feet. The additional space allows for more freedom of movement but also more dead air space, so they may not insulate quite as well as a mummy bag. However, their roomier and more comfortable fit can lead to a better night’s sleep for some. Rectangular bags are a good option if you feel claustrophobic in narrower mummy bags.

In very cold weather, a mummy bag may have a slight edge for maximum warmth. However, comfort is also essential for a restful sleep during subzero camping. The ideal solution could be a semi-rectangular or “modified mummy” bag that provides extra room in the shoulders and hips while still tapering at the feet. Some bags also have adjustable shoulder baffles to customize the width.

For subzero temperatures, the fill power and amount of insulation are most important for keeping you warm regardless of the shape. However, the cut and fit of a sleeping bag can affect how efficiently it retains heat and how comfortable you remain overnight in frigid conditions. Choosing between a mummy versus rectangular subzero sleeping bag ultimately comes down to your specific needs, preferences, and sleeping position. With the range of options available today, you can find a design that balances maximum warmth and comfort for your adventure.

Additional Features to Consider for Extreme Cold

Sub zero Sleeping Bag

Sub zero Sleeping Bag

When selecting a sub zero sleeping bag for extreme cold, additional features can help ensure your safety and comfort. Look for the following:

Insulation Type

For subzero conditions, choose a bag with 600 to 800 fill power down or synthetic insulation like PrimaLoft to provide maximum warmth without excess weight. Down fill power indicates the amount of space one ounce of down clusters occupies, so higher fill power means greater insulation for the weight. Synthetic insulation performs even when wet and is a good option if down is not suitable.

Temperature Rating

Check the EN lower limit rating, which indicates the lowest temperature at which a standard male can sleep comfortably in a relaxed position. For extreme cold, choose a rating of at least -20°F or lower. Some bags list a “comfort” and “extreme” rating to indicate a range. For maximum safety, choose a bag rated at least 10 to 15 degrees lower than the coldest temperatures you expect to encounter.

Shell Material

A durable, water-resistant shell protects insulation from the elements. Look for a ripstop nylon shell treated with a water-repellent finish like DWR. A breathable shell prevents excess condensation buildup inside the bag.

Draft Collar

A draft collar, draft tube, or neck baffle is an insulated collar around the opening of the bag that seals in warmth and prevents heat loss around your neck. For extreme cold, a draft collar is essential.

Other Features

A hood, ideally insulated, helps retain heat around your head. A thick zipper guard prevents snags and heat loss through the zipper. Loops or pockets allow you to attach a sleeping pad to the bag. An insulated footbox provides extra warmth for feet and toes. Pockets give you a place to warm hands. Straps or pads prevent the fill from shifting. A compression stuff sack allows for compact storage in your pack.

With the proper insulation, temperature rating, and additional features like a draft collar and insulated hood, a high-quality subzero sleeping bag can help ensure you stay warm even in extreme cold conditions. Choose a bag suited to the coldest temperatures you expect for maximum safety and comfort.

Top 5 Sub zero Sleeping Bags Reviewed

1. Our Top Pick: The North Face Inferno -40 Degree Sleeping Bag

This is one of the warmest sub zero sleeping bags available and is rated for extreme cold. It is designed for temperatures as low as -40°F/-40°C, making it ideal for winter camping and mountaineering.

The Inferno uses 800-fill goose down for superior insulation and loft. The down fill is treated with a water-repellent finish to maintain warmth even in damp conditions. The shell is made of ripstop nylon for durability. An insulated draft tube, insulated hood, and collar help seal in body heat.

This mummy-style sleeping bag weighs 9 lbs. 15 oz., so it may be too heavy for long treks. However, for stationary winter camping, the Inferno’s extreme warmth is worth the extra weight. It comes with a stuff sack for storage and a large mesh storage sack. The Inferno is pricey, typically retailing for $1,000, but for serious winter adventurers, it’s a worthwhile investment.

Superior Insulation

The North Face Inferno -40 Degree Sleeping Bag is designed to keep you warm in extreme subzero temperatures. It features 800 fill goose down insulation that provides an excellent warmth-to-weight ratio. The down fill is responsibly sourced according to the Responsible Down Standard (RDS) to ensure humane treatment of animals. This high quality down fill is extremely compressible yet provides superior insulation. The sleeping bag also has a draft tube along the zipper and an insulated hood to prevent heat loss.

Water-Resistant Shell

The shell is made of ripstop nylon with a durable water-resistant (DWR) finish to repel moisture. This is important for subzero conditions where any water or condensation can sap body heat. The water-resistant shell, combined with the down fill, allows this sleeping bag to provide insulation even in damp, cold environments.

Other Features

This sleeping bag has a full-length zipper and an anti-snag slider for easy access and exit. It comes with a compression stuff sack for compact storage. It is available in left- and right-hand zipper options to suit your preferences. The dimensions are designed to accommodate most body types for maximum comfort.

Our Verdict

For extreme subzero camping, the North Face Inferno -40 Degree Sleeping Bag is an excellent choice. It provides superior insulation through high-quality down fill and a water-resistant shell. The responsibly-sourced down, full-length zipper, and compression sack make this a premium product built for maximum comfort and performance in frigid temperatures. If staying warm in extreme cold is your priority, this sub zero sleeping bag is worth the investment. Overall, this is our top pick for a premium sub zero sleeping bag.

2. Runner Up: Mountain Hardwear Lamina -30 Degree Synthetic Sleeping Bag

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Design and Materials

The Mountain Hardwear Lamina -30 is designed for extreme cold weather camping and hiking. It features a mummy-style hood, draft tube, and insulated draft collar to seal in body heat. The shell is made of ripstop nylon with a water-resistant finish to repel moisture.

Synthetic Insulation

Unlike down fill, the Lamina uses synthetic Thermic Micro insulation which provides excellent loft and insulation even when wet. The insulation is rated to keep the average sleeper comfortable in temperatures as low as -30°F. For additional warmth, the sleeping bag can be zipped together with a compatible model to create a two-person bag.

Other Features

The Lamina -30 has a full-length zipper and an interior pocket to store small essentials. It comes with a stuff sack for compression and a large storage sack. At just over 6 pounds, this sleeping bag is lightweight for a subzero model but may still be too heavy for ultralight backpackers. It is best suited for winter camping, snowshoeing or other activities where weight is less of a concern.

Pros and Cons

Some benefits of the Mountain Hardwear Lamina -30 are:

  • High quality, durable construction for extreme conditions
  • Synthetic fill provides insulation even when wet
  • Mummy shape and draft features help retain body heat

Some potential downsides to consider:

  • May be too warm for mild winter weather
  • Relatively heavy and bulky compared to higher-end down bags
  • Synthetic fill requires more frequent replacement than down

For the price, the Mountain Hardwear Lamina -30 Degree Synthetic Sleeping Bag is a high-performance option for winter camping in frigid temperatures. While not the lightest or most compact, it provides dependable insulation and comfort when the mercury drops below zero. For casual winter campers on a budget, this synthetic sleeping bag represents an excellent value.

3. Budget-Friendly Option: Kelty Cosmic 0 Degree Down Sleeping Bag

The Kelty Cosmic 0 Degree Down Sleeping Bag is filled with 600 fill power duck down, which provides excellent insulation for its weight. The down fill is responsibly sourced and treated with a water-repellent finish to maintain loft even in damp conditions. The fill is distributed throughout the bag to prevent cold spots.

Thermal Comfort

This sleeping bag uses a differential cut to maximize thermal efficiency. The contoured hood, draft tube, and insulated draft collar work together to seal in body heat. A two-way locking zipper allows you to ventilate as needed for temperature regulation. The sleeping bag is designed to keep the average sleeper comfortable in temperatures as low as 0° Fahrenheit.

Durable & Packable

The Cosmic 0 Degree Down Sleeping Bag features a durable nylon ripstop shell with a water-resistant finish. The shell material is breathable yet resistant to tears and abrasions. When not in use, the sleeping bag compresses down into the included stuff sack for easy storage and transport. The total packed weight is under 4 pounds, making this a good option if you want an affordable bag for backpacking.

Additional Features

  • Zipper guard to prevent snags
  • Interior pocket for small essentials
  • Adjustable hood drawcord
  • Lifetime warranty

The Kelty Cosmic 0 Degree Down Sleeping Bag provides exceptional value at its price point. For budget-conscious campers and backpackers looking for an entry-level subzero sleeping bag, the Cosmic 0 Degree is a high-quality option worth considering. With responsible down fill, a comfort rating of 0° F, and a packable design, this sleeping bag has all the features you need for winter camping without the high cost of other premium bags.

4. Marmot CWM -40 Degree Down Sleeping Bag

Marmot’s CWM bag is rated to -40°F and filled with 800-fill goose down. The down fill and draft tube construction provide maximum insulation for extreme low temperatures. The shell is made of ripstop nylon with a DWR finish to repel moisture.

This mummy bag weighs 8 lbs. 6 oz. and comes with a stuff sack for easy storage. It is a high-quality, durable sleeping bag but more affordable than some competitors at around $700. Marmot’s lifetime warranty provides peace of mind for long-term use.

For winter trekking, the CWM’s combination of extreme warmth, reasonable weight, and lower cost make it an excellent choice for budget-conscious adventurers facing frigid conditions.

5. Western Mountaineering Versalite 10°F Down Sleeping Bag

The Versalite from Western Mountaineering is a high-performance subzero sleeping bag rated to 10°F. It uses premium 850-fill goose down for an excellent warmth-to-weight ratio. The shell is made of lightweight, breathable nylon ripstop with a DWR coating.

At only 2 lbs. 13 oz., the Versalite is ideal for winter backpacking. It features an insulated draft tube and collar and a close-fitting hood to maximize warmth. The Versalite is very compressible and comes with a stuff sack for easy packing.

While not as extreme as the Inferno or CWM, the Versalite’s combination of lightweight, premium materials, and 10°F rating make it a top choice for winter camping and backpacking. It does come at a high price, typically $700-$800, but for serious winter recreation

FAQ: Your Questions About Subzero Sleeping Bags Answered

Sub zero Sleeping Bag

Sub zero Sleeping Bag

What temperature rating do I need for extreme cold?

For subzero temperatures, you’ll want a sleeping bag rated for at least -20°F or lower. The rating refers to the lowest temperature at which a average sleeper can stay warm, so go 10-15°F lower for maximum comfort. Look for bags filled with goose down or synthetic insulation like PrimaLoft, which provide excellent insulation for their weight.

How much does a high-quality subzero sleeping bag cost?

High-performance sub zero sleeping bags typically range from $200 up to $1000 or more, depending on the materials and features. Goose down fill is very lightweight and compressible but more expensive than synthetic fill. Additional features like water resistance, draft tubes, and insulated hoods, collars and footboxes will also increase the price. For extreme cold, expect to pay $500-$1000 for a top-quality bag.

What other features should I consider?

For subzero conditions, essential features include:

  • An insulated hood that cinches snugly around your head to retain body heat.
  • A draft collar that seals the area around your neck and shoulders.
  • A full-length zipper draft tube that blocks heat loss along the zipper.
  • An insulated footbox for maximum warmth.
  • Water-resistant or waterproof outer shell to keep moisture out.
  • A mummy-style shape that is wider at the shoulders and tapers at the feet. This minimizes dead air space and heat loss.
  • Loops or straps to secure the sleeping bag in place inside a tent.

How do I stay warm in extreme cold?

To stay warm in a sub zero sleeping bag:

  1. Wear thermal base layers, socks, hat and insulated boots to bed.
  2. Use a sleeping pad for insulation from the cold ground.
  3. Cinch the hood, draft collar and any adjustable openings to trap body heat.
  4. Zip the bag up fully for maximum insulation. Only unzip if overheating.
  5. Use a bivy sack or tent to block wind and keep precipitation off the sleeping bag.
  6. Consider using a sleeping bag liner for extra warmth.
  7. Exercise before bed to increase your body temperature. Stay hydrated and eat high-energy foods.
  8. Use a hot water bottle. Fill with warm water and place in your sleeping bag before getting in.
  9. Sleep close to a companion for shared body warmth. But don’t overcrowd the sleeping bag.
  10. Get up and move around if you start to feel very cold. Do some light exercise like jumping jacks to warm up before getting back in the sleeping bag.


As you have seen, there are many factors to consider when choosing a sub zero sleeping bag for extreme cold weather camping. The most important are insulation type and fill power, temperature rating, and additional features like draft tubes, insulated hoods, and water-resistant shells. Any of the bags reviewed here would serve you well on a frigid night under the stars, but for the best combination of warmth, comfort, and value, the North Face Inferno -40 is your top choice. When the temperatures plunge far below freezing, you’ll appreciate its water-resistant, windproof shell, 800-fill goose down, and comfort rating of -40 F. For staying cozy in the coldest conditions, you can’t beat the Inferno. Now get out there and enjoy your winter adventure – and stay warm!