Understanding Sleeping Bag Temperature Ratings
Trying to understand which temperature rating you need in a sleeping bag?
You’re in the right place! In this guide, we will be covering the following:
- Sleeping bag temperature rating systems, including EN & ISO standards
- Comfort, limit, and extreme ratings
- Advice on seasonality
- The importance of a sleeping pad
- How to choose the right rating
- Tips for staying warm in your sleeping bag
A sleeping bag can make or break your camping trip, so bringing the right one along is essential. But trying to choose the best one for you can feel like navigating a maze. At every turn, you are bombarded with different information about temperature ratings, comfort and extreme limits, and season ranges.
In this guide, we break down sleeping bag temperature ratings and more. You’ll learn how to understand temperature and seasonality ratings on any bag. We’ve also included tips for making the perfect choice for you and tricks on how to stay warm inside your sleeping bag.
- Go low – It’s best to buy a bag with a ‘limit’ rating at least 5 degrees below the coldest temperatures you expect or might encounter
- Temp ratings take precedence – Season ratings can give you a rough idea of what conditions a bag is suitable for, but temperature ratings are more reliable
- Pack that pad – Sleeping pads are every bit as crucial to an effective sleep system as a sleeping bag
Table of Contents
- Understanding Sleeping Bag Temperature Ratings
- Key Takeaways
- Temperature Rating System for Sleeping Bags: EN & ISO Standards
- Comfort, Limit, and Extreme: What do they Mean?
- The Importance of a Sleeping Pad
- Which Temperature Rating Do I Need?
- Further Tips for Staying Warm in Your Sleeping Bag
- Sleep Tight!
Temperature Rating System for Sleeping Bags: EN & ISO Standards
For many years, each sleeping bag manufacturer had its methods for testing and rating the bags they made. During this time, there was no way to compare ratings between different brands or ensure a bag would work at its stated temperature rating. Since then, the industry has devised a way to standardize temperature ratings for sleeping bags using the EN or ISO systems.
EN, or European Norm, was the original method for testing temperature ranges in sleeping bags. Although no longer in use, EN standards compare closely to ISO standards.
Since 2017, most sleeping bag manufacturers have used the ISO or International Standardization Organization for testing and rating sleeping bags. ISO testing uses an almost identical method to EN testing.
Both systems test sleeping bags using a heated manikin wearing long underwear base layers and a hat. The heated manikin lies on a closed-cell foam pad. These rigorous tests establish the range of outside air temperature at which the bag will work effectively. The range runs from comfort to extreme.
Comfort, Limit, and Extreme: What do they Mean?
If you’ve been looking at high-quality sleeping bags recently, you probably noticed labels that include comfort, limit, and extreme ranges. But what do these mean?
The comfort rating refers to the temperature at which cold sleepers or the average woman will sleep comfortably through the night. This is the rating found on women’s bags.
Limit indicates the temperature at which a warm sleeper or average man will sleep comfortably through the night. Limit ratings are used on men’s bags.
Men’s and women’s bags use different ratings because research indicates that the average woman will feel colder than the average man in the same bag. Women typically have less muscle mass and evaporate less heat through the pores in their skin, so many feel colder than men both during the daytime and at night.
The extreme rating refers to the lowest possible temperature at which the bag will keep someone alive and without frostbite.
When choosing, focus on the limit and comfort rating. You don’t want camping to feel like a survival situation.
Seasonality is another way to determine temperature ranges. The seasonality rating is more general than the EN/ISO ratings. However, it can still provide useful information about the time of year and at what temperatures a bag will keep you warm and comfortable.
A two-season or summer bag should keep you comfortable from late spring to early fall or between 0°C/32°F and 5°C/41°F. As with EN/ISO ratings, seasonality ratings cannot account for all the variables. For example, elevation and weather conditions can affect temperature regardless of the season.
You may be camping in the middle of summer but at a high altitude in the wind. Under these weather conditions, a two-season model might not be appropriate. Always check the weather before a camping trip.
Our favorite 2-season bag is the Klymit KSB 35. The KSB 35 is made with 650 fill-power down that’s treated with a DWR coating for moisture resistance. It’s at the warmer end of the scale for 2-season bags and, as such, is great value for money.
Three-season bags usually have a lower limit of around -5°C/23°F. They will keep the average person comfortable from early spring through late fall.
A three-season bag might be uncomfortably warm during the summer months. If you’re going out mid-summer or at lower elevations and expecting warmer conditions, then it may be best to opt for a two-season bag. Bear in mind, however, that a three-season model will give you a little more leeway and you can always cool down by using the bag’s “AC” system – i.e., the zipper!
Four-season sleeping bags are made to keep you warm during winter camping trips at lower elevations. These bags typically have a lower limit of -10°C/14°F. For most casual winter campers, 4-season bags are sufficient.
Our favorite 4-season model is the Western Mountaineering Kodiak MF, which boasts an outstanding warmth-to-weight ratio and is sure to keep you toasty on winter nights almost anywhere in the Lower 48.
Five-season bags are designed for extreme winter camping, like high-elevation mountaineering or Arctic Circle expeditions. The lower limit ratings for these bags is normally around -40°C/-40°F. Made with the warmest materials available, a good five-season model can cost an arm and a leg. But if you’re headed into temperature extremes, it’ll be worth having.
The best 5-season bag you can buy? In our opinion, it’s hard to beat the brilliant Marmot CWM, whose résumé boasts glowing references from several Everest summiteers.
The Importance of a Sleeping Pad
We cannot stress the importance of a sleeping pad enough. A pad can make outdoor sleeps much more comfortable, but most importantly, it will insulate you from the ground. Laying directly on the ground results in a heat transfer from your body into the ground and makes you very cold.
Remember, EN and ISO temperature ratings use a closed-cell pad during laboratory testing. The temperature range of a bag reflects sleeping pad use. Without the appropriate pad, you might as well throw the temperature rating out the window.
Pads also have an insulation rating system, the “R-value”. R (resistance) values measure the ability of a flat object to resist the conductive flow of heat. Construction materials like windows and housing insulation also use R-values.
With pads, the R-value indicates how well a pad will insulate you and your body heat from the ground. The range is 1 to 7. 1 denotes something thin, with little insulation that you could use in the summer.
Three-season pads have an R-value of 3-5. The other end of the range, 5+, is reserved for winter and four-season sleeping pads. R-values are additive, meaning if you stack multiple pads, you get more insulation and extra warmth.
Long story short, the right sleeping pad is a must-have. Consider R-values and sleeping bag temperature ratings when assembling your camp sleep system.
Which Temperature Rating Do I Need?
The most important factor to consider when choosing a temperature range is the expected temperature where and when you will be camping. There are, however, a few other things to consider.
The shape and fit of a sleeping bag can affect its actual temperature rating. Bigger bags might run colder than their temperature rating suggests. Larger fitting bags have empty space, meaning they will take more energy to warm up.
If you move around at night or prefer acrobatic sleeping positions, you might need a roomier bag and a higher temperature rating.
How Do You Run?
We don’t mean what’s your form when you’re out for a jog, but whether you tend to be warm or cold at night. Some people always seem to be hot, even on cold nights, while others have to bundle up in the middle of summer.
Your personal thermostat depends on age, sex, and muscle mass. This can impact which temperature rating you need. If you run cold, get a higher-rated and warmer model. If you sweat during a snowstorm in the dead of winter, find a model with a lower temperature limit.
Consider your camping plans, both short and long-term. Are you someone who routinely goes snow-caving or on a winter camping trip? Or do you usually go car camping? Are you a summertime weekend warrior or a shoulder-season adventurer?
Buy a model with a rating tailored to your normal use. If you have no idea where to begin and don’t want to buy multiple bags, consider getting a three-season model in the 20°F range. This will cover most of your bases and give you the right balance of warmth and flexibility.
Further Tips for Staying Warm in Your Sleeping Bag
1. Choose A Warmer Bag Than You Think You’ll Need
You can always cool down at night by unzipping, delayering, or opening a vent. However, once you’re cold, it can be difficult to warm back up. The take-home? Choose a warmer model than you think you need.
In other words, choose one with a lower rating than the lowest temperature where you plan to camp. If you plan to go winter camping in the high alpine desert with colder temperatures (in the mid-twenties, say), bring a three or four-season bag.
2. Layer Up
This one hopefully goes without saying: layer up! Clothes add insulation and warmth to your sleep system. Wear long underwear, warm socks, and a hat when you go to bed if conditions require.
For chillier nights, wear a light mid-layer like a sweatshirt with a hood or a fleece over your base layer. If you’re concerned about being cold, there’s no rule against wearing a down jacket to bed, either. You can always take it off and use it as a pillow when you warm up. With the proper layers, you’ll be toasty in your tent!
3. Do a Pre-Sleep Warm-Up
One way to increase body temperature is through exercise. This isn’t to say you should go for a jog before hitting the hay, but light-intensity exercise can help warm you up. Try some easy stretching or yoga poses in your tent. Laps around camp or slow-mo high knees can also increase body temperature.
The last thing you want is to go to bed sweaty, which will make you much colder! Keep the activity level low and controlled during your pre-sleep warm-up.
4. Eat Late
Body temperature increases about 20-30 minutes after eating. This is because you burn energy as your body’s digestive system goes to work. Snacks that take longer to digest will keep you warmer longer. Peanuts and peanut butter make great bedtime snacks.
Bananas, whole milk, and hard cheeses also take a while to digest. If you can wait to eat until right before bed, have a full meal. Eating 30 minutes before bed will help you stay warm while you sleep.
5. Have a Hot Drink
Hot beverages can also warm you up before bedtime. Avoid anything caffeinated when you’re trying to sleep. Opt for caffeine-free tea or hot chocolate. Ginger root is known to have hyperthermic effects, so having ginger tea before hitting the sack is a good way to help yourself nod off.
Not only will a hot drink increase your body temperature before bed, but holding a hot mug can help warm up your hands.
6. Bring a Hot Water Bottle
Some winter camping experts swear by the hot water bottle trick. You can use your Nalgene or a hot-water-specific bladder. Fill the bottle/bladder with hot water and put it at the bottom of your bag. This can be a game-changer for cold sleepers and those with chronically icy feet.
If you try this tip, there are important things to remember. First, really tighten the lids. Getting water on your bag defeats the purpose.
Second, do not put hot water in any old bottle! Insulated thermoses won’t transfer heat. Old plastic bottles might leak or break. An exploded water bottle will make you wet and cold and could cause dangerous burns.
7. Insulate Your Underside (Use a Pad and Tarp or Mylar Blanket)
Remember, nothing steals body heat faster than the ground. Insulating your underside on any camping trip is crucial, especially if you’re venturing out on a winter camping adventure.
As discussed, sleeping pads are essential. You can also insulate your underside with a tarp or Mylar emergency blanket. Tarps and tent footprints offer a level of insulation from the ground.
Putting an emergency blanket under you and your bag can make a huge difference. Mylar emergency blankets reflect 90% of your body heat.
Mylar blankets are also lightweight and can pack down to a small size. Take one on your next backpacking trip to insulate you from the ground and keep you warm at night.
8. Keep Condensation to a Minimum
Down sleeping bags are lightweight and warmer than their synthetic counterparts. Their only downfall is moisture. Down performs poorly when damp, so it’s imperative that you keep condensation to a minimum. There are a few ways to do this:
- Pitch your tent on dry ground (under trees if you can, the air under trees is warmer)
- Stake your rain fly out as taut as possible
- Ventilation is your friend; open tent and rain fly vents (weather permitting)
9. Use a Sleeping Bag Liner
Sleeping bag liners are, essentially, silk or microfiber sacks that go inside your sleeping bag. They come in various shapes and materials, but all work to add comfort, insulation, and warmth to your sleep system.
Some liners add up to 25°F of temperature rating to sleeping bags. Liners are perfect if you’re unsure how cold it will be or if predicted temperatures are between two ratings.
A sleeping bag is arguably your most important piece of outdoor gear. Without the proper temperature rating, you might end up in your tent shivering while everyone else enjoys a good night’s sleep.
We hope our guide to understanding sleeping bag ratings has made finding the right one for your needs easier, and wish you the best on all those outdoor sleeps to come!
If you have any questions feel free to drop them in the comment section below. And don’t forget to share this with your camper friends!