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Winter Sleeping Bags

Quality sleeping bags can cost a lot of money and are one of the heaviest items in your backpack. When you make this purchase, the best outcome is the lightest sleeping bag that still meets your requirements and budget.

How to Choose a Sleeping Bag for Pacific Northwest Winter Backpacking

If you are use to camping in summer and the shoulder seasons and are wondering what type of sleeping bag you’ll need for winter use in the Cascade Mountains here in Washington State, here are some basic points to consider.

Picking the Temperature Rating

The first thing you need to do is to determine the temperature rating you need. Winters in the Pacific Northwest are mild compared to other regions this far north. One way to determine likely temperatures is to study the average temperatures at different elevations on major peaks throughout the Cascade range. For me, the best potential campsites will start around 3000 ft, but in most instances, I end up camping around 4500–7500ft. I’ve only camped twice at higher elevations (Camp Muir at 10,000ft and Mount Adams at 12,ooo ft). Here in Washington State, if you look at temperatures on peaks North and South, West and East, you find that temperatures tend to be colder on the Eastside, as well as further North.

For planning purposes, I have formulated four typical scenarios:

Shoulder season averages (common): 25º to 45º F (September–November/March–June)
Winter averages (common): 25º F to 35º F (November–March)
Winter coldest averages (common): 10º to 25º F (September–June)
Winter deep cold averages (rare): –0º F to 10º F (occurring mostly December–May)

Notice, that 0º F weather is rare. It is so rare, I have never recorded it on any of my trips.

Shoulder Season snow conditions
Left: First snow in September 2019 using a zero degree sleeping bag. Right: Snow at around 7500 ft at the end of June 2020, using a 15ºF sleeping bag.

Based on this data, a 0º F sleeping bag will be sufficient for most trips throughout the Pacific Northwest winter season. I don’t often use a thermometer, but the coldest thermometer temperature I have ever recorded is 6º F while camping on a frozen lake on the East side of the Cascade Mountains at about 5000 ft (March, end of winter). Because the expected temperature was going to be close to zero, I took a –20º F expedition sleeping bag, which allowed me to sleep comfortably with no concerns.

winter camping in deep snow
Once the snow falls get deeper and colder, I often choose a –20 Expedition sleeping bag, even though temperatures rarely fall as low as 10º F. Most people who join me only take a lighter 0º F sleeping bag.

In the shoulder seasons (spring to early summer/late summer to fall) a 15º F sleeping bag will usually be sufficient. For rare deep cold nights, an “expedition” category –15º or –20º F sleeping bag will keep you comfortable. If you can only budget for one winter sleeping bag, get the 0º F option. If you are fully committed to winter backpacking and only want to carry what each trip requires, then you’ll want three sleeping bags, a 15º, a 0º, and a –20º F. With this range you will be covered for most every possible scenario, and never need to carry more weight than circumstances require.

If you are a cold sleeper, which is certainly the case for myself, then I recommend the 10–15 degree rule. That is, always have a sleeping bag that is rated 10–15 degrees warmer than the expected forecast. If the forecast is 15º F, then a 0º (lower limit) sleeping bag is the best option. If you have a 0º bag, there are very few times when a trip will have an expected lower limit beyond your gear capabilities.

Regardless of the sleeping bag you have, always check the mountain forecast carefully. Freakish lows are extremely unusual but they can occur. Back on 30 December 1968, Mazama and Winthrop recorded –48°F.

–20º F expedition sleeping bag
Know your limits. For me, –5 to –10º F are my gear limits. For any forecast approaching less than 10º F I use a –20 Expedition sleeping bag. A 0º F sleeping bag is lighter and will do the job, but I tend to sleep cold so I prefer the extra warmth and comfort.

How Sleeping Bags are Rated

Down insulation is rated based on the number of cubic inches of loft one ounce of down produces. The loft is the primary way down captures and holds the warmth generated by your body. Down doesn’t generate warmth, it merely helps preserve the warmth your body generates. Most sleeping bags use 550–900 fill power ratings. 550 provides the lowest thermal performance and 900 the highest. But you must look at other factors too, such as how much down is used, how the bag is designed (baffle construction and draft tubes), and overall fabric quality.

0º F Down Sleeping Bag Examples

Zero-degree sleeping bags are the optimum bags for Pacific Northwest winters, so I will focus on some of the leading examples with that rating. The table below shows only 0ºF rated duck and goose down sleeping bags. Notice that the higher-rated down is lighter but more expensive. To simplify, all bags are the men’s or unisex version and in the regular size. (Some bags are available in long sizes and the Mountain Equipment Glacier 1000 model and the Sierra Designs bags are available in a women’s version. There are not many companies that offer Zero and Expedition-level sleeping bags tailored specifically for women.

table showing zero-degree sleeping bags compared
This table shows leading 0º F rated sleeping bags. Notice that as the fill power goes up, so does the price, but the total weight falls.

If you are on a budget, the Sierra Designs Nitro (available in a women’s version) and the Therm-a-rest Oberon are very good options. Both are in the lower price range, use 800 down, and ultra-light materials. Western Mountaineering and Feathered Friends use higher fill power and put slightly more focus on durability rather than the most ultra-light materials.

A company called Hyke and Byke (not included in my table above) offers several zero-degree down sleeping bags in the $170–230 range. I know one backpacker who uses one of these and he seems content with it. Is the down responsibly sourced and it is a quality product? I don’t know. The actual down fill amounts are not posted and there is no independent rating or certifications.

This article is just about winter sleeping bags, but I would like to mention one shoulder season option too. For warmer trips, my own go-to preference is the REI Magma 15º F, which is available in a women’s edition too. This bag is 850-fill-power goose down, and for an ISO comfort rating of 28º F, it only weighs 1 lb 13 oz, which is an impressive warmth-to-weight ratio. It is around $380–400, but you can likely get one on sale. I often take the REI Magma 15 even when the forecast puts temperatures close to 50ºF because my 40º F sleeping bag is not any lighter. If there is no weight saving from the cooler bag, I would rather have the extra back-up warmth.

Down vs Synthetic

The alternative to down is synthetic. Synthetic filling is less effective at capturing warmth than down. It is also bulkier, making it harder to pack, and it doesn’t retain loft for as long. Despite these disadvantages, synthetic sleeping bags have two important advantages. First, they provide more loft and warmth if they become wet from rain or heavy tent condensation, and second, they are much more affordable. The table below shows two synthetic 0º F sleeping bags compared with an equivalent down version. Notice the weight and price difference.

If you are on a limited budget or are unsure if winter backpacking is something you will enjoy, a synthetic 0º F bag might be a good option to consider. It’s how I got started!

Quite often in the Pacific Northwest, temperatures are slightly above freezing, making condensation a problem for Down sleeping bags.

drying a winter sleeping bag
Airing out my down sleeping bag in the sun. There are plenty of days in the winter when you do not have the luxury of drying out a down sleeping bag.

Even if it is 20–25º F, temperatures inside a tent may be above freezing. In such conditions, a 15º F synthetic sleeping bag could be more effective than a down bag on multiple night trips, especially in the shoulder season.

Sleeping bag Packability
Notice how much larger the synthetic sleeping bag is to the down one. Both bags on the left are 0º F sleeping bags. The down option is in a slightly compressed compression sack and the synthetic option can be compressed to a similar size using the same compression sack, but requiring greater effort. In fact, all these large bags, including a –20 Expedition sleeping bag can be compressed further than the size shown here (2nd on the left). However, extreme compressing is not good for the sleeping bag’s longevity. My winter backpack is 58 liters (good for 2–5 day trips) and these large sleeping bags do take up considerable room.
This table shows two 0º F synthetic sleeping bags compared to a 0º F down sleeping bag. The synthetic sleeping bags are nearly twice the weight. However, the price for the synthetic options is dramatically less.

Lower Limit vs. Comfort

Sleeping bags have two ratings, the “lower limit” and the “comfort” rating. Manufacturers usually, but not always, feature the lower rating in the name of the sleeping bag. I always focus on the comfort rating when trip planning because I am a cold sleeper. If the sleeping bag is listed as a 30ºF sleeping bag, then the comfort rating is likely to only be around 40 to 45º F. If the weather forecast is 30º F at the planned elevation, then a 15º F lower limit rating is required for comfort. If the weather forecast is 15º F at the planned elevation, then a 0º F is required for comfort. If the weather forecast is 5º–0º F at the camp elevation, then a –20º F expedition sleeping bag is required. Bear in mind that once the forecast gets near 0º F it is wise to overcompensate. The forecast can easily be off by 10º and the lower the temperatures go the more important it is that you have gear that will keep you comfortable and secure. My own rule is to carry a sleeping bag that is rated 10º to 15º degrees below the forecast. This, however, is not a rule that fits everyone.

How Ratings are Determined

Some sleeping bag ratings are merely manufacturers’ claims. The first REI 0º sleeping bag I bought was shortly after reclassified as a 10º sleeping bag, before being discontinued. Nowadays, most major manufacturers have their sleeping bags rated independently using the European Norm (EN) 13537 and/or the International Organization for Standardization (ISO) 23537 testing methods. These protocols rate each bag for Comfort and Lower Limit. The Comfort rating refers to the lowest temperature the average “cold sleeper” will be comfortable, and the Lower Limit rating refers to the lowest temperature the average “warm sleeper” will be comfortable. This rating assumes the person is wearing an underwear base layer (top and bottom and a beanie) with a 1-inch thick insulating pad underneath the sleeping bag.

Some brands use the Comfort rating for women’s bags and the Lower rating for men’s and unisex bags when naming the bag. This means you cannot assume the lower limit rating is below the rating in the name. You must check the EN and ISO ratings instead. Also, be aware that some brands still don’t use the EN or ISO rating system. It is a useful system for comparing different brand models.

Ratings for Women vs Men

“Lower limit” and the “comfort” ratings mean different things for different people because everyone’s body and sleep comfort are not the same. It is generally assumed that men require less warmth than women, but clearly, some men require more. You must know your own requirements.

As mentioned above, some brands use the Comfort rating for women’s bags and the Lower rating for men’s and unisex bags. As an example, consider the REI “Zephyr 20 Sleeping Bag.” The women’s version is rated 22º F for comfort and the men’s version 21º F for the lower limit. Both are “Zephyr 20,” presumably meaning 20º F sleeping bags, but the men’s version has 15 ounces less insulation. Both cost the same and both are for 20º F, but the men’s version is lighter and less insulated. I would only consider the Zephyr for summer use, but I mention it here just to show an example of how a Women’s and Men’s sleeping bag compare.

Other manufacturers approach the issue differently. Mountain Equipment, for example, offers a model called the “Glacier 1000” in both a women’s and men’s versions. Both have the same EN rating, but the men’s version has more rather than less insulation, and Mountain Equipment has its own “Good Night’s Sleep rating,” which is 7 degrees warmer for the men’s version, even though it contains only 2 oz more down. It is nice that Mountain Equipment has decided to create cold-weather sleeping bags for women, but before one makes much of this, note that when comparing the two bags together, there doesn’t appear to be any differences in the tailoring. Both the men’s and women’s versions have shoulder girth of 62 inches and a hip girth of 54 inches. Color and 2 oz difference in fill are the only things that distinguish the versions.

Sierra Designs are even more identical:

I have known men and women who say they use 0º F sleeping bags in 0º F weather and are comfortable. I’m not sure if they were accurately determining the temperatures they were experiencing, but I do know that this would not work for me. I never plan to use a sleeping bag in a situation where the lower limit matches the expected temperature. I always plan for 10–15º of extra warmth, without considering other factors such as hot water bottles, warmth captured by my tent, or additional insulated clothing.

One thing is certain, there is no consistent rule for distinguishing women’s and men’s sleeping bags. For example, the REI Co-op Zephyr 20 Sleeping Bag, there is 15 oz less down in the men’s version, but in the Mountain Equipment Glacier 1000 Sleeping Bag, there is 2 oz more. With the Sierra Designs Nitro, the specs are the same. This means it is not always the case that manufacturers make one gender more insulated than another, but rather that each manufacturer has its own approach.

When almost everything is the same, there is still somehow a slight difference in final weight. This is likely because the women’s sleeping bag uses the same materials for a slightly shorter bag. My advice is to not concern yourself with gender labels and instead match your body and needs with the specifications that work best for you. For examples, here are the three available sizes for the Sierra Designs Nitro:

Fits Up To: 5′ 8″ / 173 cm
Length: 74in / 188 cm
Shoulder Circumference: 58″ / 147 cm
Hip Circumference: 58″ / 147 cm
Footbox Circumference: 39″ / 99 cm

Fits Up To: 6′ 0″ / 183 cm
Length: 78in / 198 cm
Shoulder Circumference: 62″ / 157 cm
Hip Circumference: 56″ / 142 cm
Footbox Circumference: 40″ / 102 cm

Fits Up To: 6′ 6″ / 198 cm
Length: 84in / 213 cm
Shoulder Circumference: 64″ / 163 cm
Hip Circumference: 58″ / 147 cm
Footbox Circumference: 42″ / 107 cm

One of these is the women’s version. But does gender matter? All use the same colors. Even if you are a woman who can fit perfectly in the woman’s option, you might want to choose the next size up for the extra space to put your boots at the bottom to keep them from freezing over night.

Finding the Right Fit

If you can, visit a gear showroom and ask to try out the sleeping bag. This will help you determine the fit and comfort of the design.

A bag that is tailored to fit your body length and shape will provide the most efficient warmth. However, having some extra space for gear such as a hot water bottle, electronics, clothing, and even boots can be beneficial. If my boots are wet from snowmelt, I bag them and put them inside the bottom of my sleeping bag on deep cold nights. This prevents the boots from freezing solid and being painful to put on the next day. If your boots are already frozen, don’t bother putting them in your sleeping bag. They will remain frozen and just keep your feet cold at night. Thaw the boots out instead with a hot water bottle in the morning.

The Total Sleeping System

A total winter sleeping system consists of:

  1. An appropriately rated sleeping bag
  2. Two sleeping mats, one solid core, one air, with a combined R-value of at least 5. More is preferable.
  3. A tent for wind protection.
  4. A complete dedicated head-to-toe base layer.
  5. A hot water bottle.
  6. Air-mattress repair patches.
Base layer clothing for winter backpacking
This photos shows complete base layer clothing (pants, top, socks, gloves, and beanie, plus a hot water bottle. In this selection, the top is smart wool and the bottle is a mid-weight Capilene. This is my selection for deep cold nights. Normally, I take a lighter nylon thermal top and bottom, instead of the hotter smart wool and Capilene.

Ideally, your air mattress alone should have 5+ R-value. The solid core mattress is primarily protection and backup. In an emergency, someone can loan their solid core, and the two solid core mattresses combined will get the person with the failed air mattress through the night. Quite often, your pack and other gear will be partially under your air mattress. The solid core pad can cover top this gear and will help protect the air mattress from anything sharp. However, it is important to check the gear for anything that might puncture the air mattress such as unclipped pack straps, stoves, stove windscreens. Some items can be wrapped in your gaiters to cover the edges.

Tips for Maximizing Warmth

Always shake out and fluff up your sleeping bag as much as possible when you set up camp. The loft helps capture your body’s warmth.

Don’t lay anything over your sleeping bag that will reduce its loft. Rather than adding warmth, it will reduce loft and that will lower the sleeping bag’s ability to capture warmth.

A 4-season tent will add about 10º of warmth if the door is closed. I usually keep the door open unless it is snowing or too windy. I enjoy the fresh air and don’t need the extra warmth. Leaving the door open also reduces tent condensation. (I’ve heard your body breathes out about a liter of water in the course of a night, but I’m not sure if that is true.) Tent condensation is a threat to the effectiveness of your sleeping bag. Down sleeping bags lose loft when wet and become ineffective. It is very important to keep the sleeping bag dry.

The purpose of the mummy bag design is to keep the warmth close to your body, eliminating extra areas for your body to heat, and sealing off ways for the heat to escape. This means that a good quality bag will have a baffle along the zipper to prevent warmth from escaping and a drawstring around the face. For this reason, rectangular designs and quilts are less efficient.

To maximize warmth, always sleep in a fresh base layer—socks, thermal leggings, thermal top (nylon, Capilene, or Smart Wool), and beanie. Avoid sleeping in clothes that you have hiked in during the day. Your hiking clothes may seem dry but are likely more moist than you realize and that moisture wicks warmth away from your body. Also, this dedicated nighttime baselayer will help protect your sleeping bag from sweat and body grim.

There are few things more enjoyable than a hot water bottle. I always carry a one-liter Nalgene bottle for this purpose. Arguably, it is not necessary. Your body will eventually warm up in the sleeping bag. However, you may not realize it if your body has lost too much warmth before sleep. A hot water bottle between the thighs and next to your main arteries will quickly restore warmth to your body and help you get a comfortable sleep. Re-tighten the lid about 10 minutes after filling the bottle. The bottle expands from the heat and the lid loosens. Keep it tight so it doesn’t leak out at night. The ability to operate a stove in high winds and harsh conditions to create a hot water bottle is a first-aid skill for hypothermia.

The foot of your sleeping bag usually has extra down to help keep your feet warm. If you are short, be sure to pull up the bag so your feet are at the bottom of the bag.

Be sure the zipper baffle is laying over the zipper to prevent warmth from escaping. Also, if your sleeping bag has a neck baffle, make sure it is positioned correctly to prevent warmth from escaping around your neck.

Your body compresses the sleeping bag under your body. This allows warmth to easily transfer to the ground. For this reason, you must have 5+ R-value insulation under your sleeping bag or the sleeping bag will be almost useless. An effective sleeping pad strategy consists of a solid core sleeping pad (usually 2 R-Value) and an air mattress (usually 3–7 R-value). Take great care to store sharp items and belt clips away from your air mattress in your pack and tent.

Sleeping bag storage

Always store your sleeping bag in a hanging position or large breathable storage sack to help retain the bag’s loft. Never leave a bag compressed for long periods because this will damage the down or synthetic fibers.

When packing the sleeping bag in your backpack, only compress the sleeping bag as much as necessary. When you take it out to use it, fluff it up as much as possible. The effectiveness of the sleeping bag depends on its loft. Eventually, sleeping bags loose loft and need to be replaced. Down sleeping bags last longer, maybe 10 years with weekend use and synthetic sleeping bags last about half that amount of time.

Some sleeping bags come with a large storage sack. You can also purchase them. Left to right: –20 expedition bag, 0 degree bag, 15 degree bag, and 2 summer bags. The storage sack that comes with the Therm-a-Rest Oberon is, in my opinion, too small. So I put my Oberon in a larger storage sack and use the Therm-a-Rest one for my summer bags.
Laundry storage sacks for sleeping bags
Laundry storage sacks are a low-cost alternative to specialty sleeping bags storage sacks. The common 36×24 inch size works for most down sleeping bags that are rated 15ºF or above and most synthetic sleeping bags rated 0º F and above but may be too small for 0º F and expedition down sleeping bags. In this photo, the laundry sacks contain 0º F synthetic sleeping bags.

Fun Facts

So what’s the warmest sleeping bag money will buy? Feathered Friends offers the Snowy Owl EX -60º F Sleeping Bag, for $1,139. This bag is described as “the warmest sleeping bag on the planet” and “the bag of choice for polar expeditions.” Thankfully, one doesn’t have to carry this 5 lb bag here in the Pacific Northwest.

What does a deep cold weather sleeping bag weigh if it is synthetic? Browning Camping makes a “McKimnley” –30º synthetic sleeping bag that weighs 12 lbs 12 oz.

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