Nothing can be more grueling than spending a long, cold night in a tent. Purchase a sleeping bag with the wrong rating for your destination or season, and you might spend hours shivering instead of snoozing. However, a variety of factors can play into sleeping bag temperature ratings, as not all users represent the “average sleeper”.
To keep warm in your sleeping bag you will need a bag that is the right temperature rating, the right insulation and shell for climate conditions, know the variables that can affect your bags warmth, know what shape is best for your trip, know what items you can use for warmth in your bag (hand warmers, water bottles work great) and know some little things that affect your warmth (urinating before bed and eating help).
In this guide we will walk you through each of these things you need to know to be at a comfortable temperature.
Here’s what we will cover to make sure you are warm and comfortable in your sleeping bag.
- Understanding sleeping bag temperature ratings
- Variables that affect a sleeping bags warmth
- Insulation and it’s effects on sleeping bag temperatures
- Shell material’s role in controlling temperature
- Choosing the right shape of your sleeping bag
- Items to help keep your sleeping bag warm
- Tips and tricks for staying warm in your bag
Understanding sleeping bag temperature ratings
- EN sleeping bag temperature ratings
The only true rating system is the EN scale or EN13537 scale. While sleeping bags with this temperature rating can be found in the U.S., there is no true rating system that has to be used in the United States. For more information on this, read the U.S. temperature ratings section.
It is possible for a three season bag to have different temperature ratings depending on things like fill and shell. This makes this rating system very helpful for determining the low temperatures that a bag can handle regardless of the materials it is made from.
- The lower limit
The lower limit is the coldest temperatures at which an average man can sleep in comfort. However, it is likely that when using the bag in conditions hovering around the lower temperature, you may feel chilled.
- The upper limit
This is the temperature at which the bag may begin to feel too warm. As you may have guessed, the comfort level is the optimum temperature for sleeping in the bag.
- The comfort temperature
This is the teperature that most people will feel comfortable at. The temperature that someone is comfortable at can vary depending on factors like clothing and metabolism. You will need to determine if you are “hot natured” or “cold natured”.
- The extreme rating
This is the lowest temperature that a person can safely sleep for 6 hours without hypothermia. However, we never recommend using a bag in temperatures that are at the extreme limit.
If we apply this rating scale to a three-season sleeping bag, we should get the following results. At 25 degrees, you will probably start to feel chilled and at temperatures exceeding 35 degrees, you may get toasty.
The median tested comfort temperature is 29 degrees, with twenty-nine degrees as the median tested lower limit, this bag would likely be suitable for the cooler nights that occur in the fall and spring.
- ISO temperature ratings
The ISO rating is and updated version of the EN rating system and will be used as the international standard going forward. The ISO rating system uses different terminology than the old EN system and we are going to break this new terminology for you.
As with the EN system, this is the lowest temperature that an average man can sleep in comfort but with anything below that temperature you may start to feel cold.
Sometimes this is used in place pf comfort but it still means this is the lowest temperature that a person can sleep at and still be comfortable.
This is the range between comfort and risk that a person would start to fill cold
This is the temperature where the risk of hypothermia is high.
- Figuring U.S. Temperature ratings
Although many manufacturers are starting to use the EN/ISO rating, there really is no standard rating for sleeping bags in the U.S. since each manufacturer uses it’s own “rating”. This means that the true temperature may not and may not be comfortable to the average man or woman. The good news is sleeping bags are generally put into 4 distinct categories and this can give you a good idea of temperature range.
With no true standard you can have two sleeping bags rated for 20 degrees but one maybe warm at that temperature while you are cold in the other at 20 degrees.
This also means that a bag rated as 3 season may feel cold at 30 degrees and another brand may feel comfortable. It is also possible for a sleeping bag to handle colder temperatures than what it is rated for. This is not common but there are many things that can affect how warm or cold a bag is. We cover the varibles in the varibles that can affect a sleeping bags warmth section.
Quick tip- For sleeping bags that use a manufacturers rating and not a standard ISO or EN rating, get a bag that is rated for 10 degrees below the lowest expected temperature duting your trip. This will help protect against ratings that are too low to begin with or if the temperatures are colder than expected.
Varibles that effect a sleeping bags warmth
Even with standard ratings, there are varibles that will have an affect on how warm a sleeping bag feels.
- A person’s health, gender, and size.
Women tend to sleep cooler than men, and children can experience more sudden and drastic temperature swings than adults. All of these variables may affect which temperature you would personally feel comfortable at in the bag.
If someone has a slow metabolism or blood pressure, a sleeping bag can feel much colder.
- What you sleep on and the postion you sleep in.
The ratings are based on the standard sleeper, sleeping in a position with arms inside the bag, wearing a base layer and sleeping on a foam mat. The rating procedures are carried out in a lab using a mannequin.
This means that in practice, the use of a sleeping pad and even your sleeping attire will skew the rating scale. Bag users in the real world may sleep directly on the ground, inside a tent, or wearing a few layers. Remember, you can always unzip the bag or use liners to change the temperature.
If you are sleeping directly on the ground or on some sort of bedding can have a dramatic affect on your bags temperature.
The clothing you wear while sleeping can have the greatest effect on a sleeping bags temprature. If you are wearing one pair of regular clothes you will be colder than if you have layers of clothing, thermals or wool clothing on.
This will not only have a negative effect on down insulation and some synthetic insulations but moisture on your skin can lead to rapid hyothermia.
Insulation and Its Effect on sleeping bag temperature
Three-season sleeping bags use one of two types of insulation, either a synthetic fill or a down fill. No matter the type of insulation, you want it to trap the heat around your body and prevent it from escaping. Down is nature’s insulator, found under the feathers of birds, typically geese.
Down fill is very durable and extremely compressible yet still quite light. It makes an excellent insulator aside from two notable downsides.
Down is not equipped to handle moisture well. Unlike the top feathers on birds that shed water and protect the down, the fill in your sleeping bag will become saturated if it gets wet. Once waterlogged, the down becomes a poor insulator, resulting in a chilly sleeping situation.
Another con is the cost, down can be expensive. However, due to its durability, this long-lasting bag could be considered an investment for the habitual camper.
An alternative to down fill is synthetic fill. Synthetic is usually composed of fibers created to mirror the properties of down. As it is not a natural fiber, there are a few pros.
Synthetic fill can be treated to be water-resistant, meaning it will maintain its warming properties even when wet. Additionally, purchasing a synthetic fill sleeping bag won’t break the bank.
There are two negatives to a synthetic sleeping bag, namely its compressibility. Unlike down, the bag cannot be stuffed into a backpack as easily. It may not last you as long either, having a shorter lifespan than a down filled sleeping bag.
For more in-depth information on insulation, we recommend you read our article Are down sleeping bags better than synthetic?
Shell material’s role in controlling temperature
You don’t want the rain to soak through your bag, but you don’t want to be swimming in your own sweat either. Shells need to be breathable, durable, and waterproof.
Shells are usually made of polyester or nylon. Nylon is the more enduring option preferred by frequent campers. Besides the ability to stand up to the elements, nylon is lightweight.
Nylon shells treated with solutions like Gore-Tex in order to be waterproof are more expensive, and for good reason. A high-quality waterproof shell is manufactured in various stages to resist liquids and humidity. The fabric will not hold moisture inside, preventing you from slumbering in a puddle, while the outside sheds water, protecting the precious fill.
These bags are also “seam-taped” so water cannot sneak in through the stitching. If you plan to sleep without a tent, a waterproof bag is advisable.
Polyester shelled bags are fine for occasional campers that don’t plan on taking the bag deep into the backcountry or getting it wet. Because of this, they are less costly than nylon shelled bags, but still make a great breathable and lightweight alternative to nylon.
As with any fabric item being used in the outdoors, it is not advisable to purchase a sleeping bag made of cotton. Cotton bags may be available and marketed as a cheaper option, but you will probably end up regretting your purchase. Cotton is awful when wet and takes a long time to dry.
Choosing the Right Shape of your sleeping bag
Three-season bags come in many forms, including mummy, rectangle, and semi-rectangular. How sleeping bags keep you warm is not rocket science. A well-fitting bag will trap heat against your body, while a loose bag will have cold pockets.
If you want a truly warm bag, go for the mummy shape with a close fit. In most cases, these bags include a hood and rolling over requires taking the entire bag with you.
If you despise sleeping in a cocoon, a rectangular bag has lots of room to spread out but might be cool and drafty. Sleepers that like to roll, but still want to be cozy may opt for a compromise between temperature and space with a semi-rectangular bag.
A compromise between a mummy and rectanular bag is the semi-rectangular bag. This will still have some of the room to move of a rectangle bag but will also provide a little of the from fit that a mummy bag offers.
Finally, sleeping bags can come in “couples” or “made for two” sizes. But understand that these may not be the warmest option, depending on how close you like to sleep to the other person. In lieu of purchasing a doubles bag, you might want to purchase two individual sleeping bags that can zip together.
Sometimes bags that can be combined are marketed as such, but you may also buy two bags of the same model and brand and they should zip. It would be a good idea to test out the latter in store so you don’t end up disappointed at the campsite.
Products to help keep your sleeping bag warm
- Sleeping bag liner
To adjust the temperature of your three-season bag to suit the conditions, you may choose to use a liner. Liners can be tailored to fit inside your bag (a mummy liner) or to supplement your bag (rectangular liners).
Mummy liners are shaped like the image that probably comes to mind, a sarcophagus. They are designed to fit easily into most sleeping bags. They provide additional warmth and a barrier to keep your bag clean.
Rectangular liners can be used inside bags as well, but don’t fit as seamlessly. They can also be used as standalone covers when your bag is simply too hot. Sometimes known as traveler’s sheets, rectangular liners can provide a barrier between you and suspect sleeping arrangements.
Liners come in a variety of materials to suit your needs. Silk and fleece provide insulation. Silk can insulate in the cold or keep you cool when it is hot. Fleece adds an extra layer of warmth.
Cotton is absorbent and relatively inexpensive, and synthetics can provide varying degrees of temperature control. Specialty insulated liners can add upwards of twenty-degrees of warmth, perfect if you are camping in frigid conditions.
Clothing can make a big difference when it comes to staying warm in your sleeping bag. Here are a few clothing items that will help you stay comfortable.
Wool socks- If you are like me, you will be warm natured for the most part but your feet are always cold. Wool socks are perfect in this situation. If you are worried about your feet getting too hot and sweating, then marino wool would be a great choice. Marino is light-weight but breathable.
Thermals- Combine thermals with a good sleeping bag and you should be able to stay at a warm temperature. Thermals are versitale when it comes to price and materials. You can even buy marino wool thermals to stay warm and dry.
Beanie- Since most of your heat is lost through you head, a beanie is a great way to add an extra layer of protection to your sleeping bag. The great thing about a beanie is if you get too hot, it is easily removed.
- Heat packs
Heat packs or hand warmers are provide an easy way to raise the temperature in your sleeping bag. Just add some to your socks or in other areas where you need some extra warmth. Heat packs are very affordable and as an added bonus, they are light-weight, making them perfect for hiniking trips.
- Water bottles
You can use these in the same way you would heat packs but you will need a source of warm water. Also, a water bottle will take up more room inside your sleeping bag.
- Sleeping pad
Sleeping pads not only add comfort but add another layer of insulation between your sleeping bag and the ground. The ground will absorb heat at a high rate and this extra layer can make a big difference.
Tips and tricks for staying warm in your bag
There are several different things you can do to
Eating something high in carbs before you tuck into your sleeping bag will raise you meabolism. When you raise your metabolism your body will produce more heat to get locked in between you and your insulation. Also, carbs break down into energy for your body to produce heat.
- Go PEE
There are two main benefits from going to pee before you get in you bag that will help keep you warm.
First, if there is urine in your bladder, it will absorb heat. When urine absorbs heat from your body, your body has to use more energy to produce heat that the urine is absorbing. You really want any energy for heat production not to be wasted.
Second, when your bladder gets full, your kidney’s will slow down on production. This production prodcues heat and when it is slowed down, so is the heat production.
- Light exercise
Getting your internal temperature up before getting in your bag will create more heat for the insulation to trap.
- Stay dry
Moisture draws heat away from your body through evaporation. Sweat, rain or just damp enviroments can cause heat loss through evaporation. In order to reduce a bodies heat loss, it is vital that your baody and clothes are dry, even if you have to dry off with a towel or change clothes.
There are many variables when choosing a three-season sleeping bag. If you hope to camp during some gorgeous fall or spring nights that are chilly but likely won’t see frost, a three-season sleeping bag is perfect for you. Don’t let your sleeping bag limit your trips though! Select the correct fill, shell, shape, and liner and you will be able to use it in a variety of settings and temperatures.
We would love to hear from you. If you have some tips, tricks or information on keeping wram in a sleeping bag or any other comments, please let us know in the comments section.
More articles you will want to read.
What are the best sleeping bag materials? ( Shell and Fill )
Why you need a sleeping bag liner.
How should sleeping bags be stored?