Perhaps you’re thinking about getting into some winter camping. Maybe you’re looking to venture out later in the Fall—or earlier in the Spring—and happen to be a cold sleeper. The question will eventually arise: What do I need, a 3-season sleeping bag or a winter sleeping bag?

At face value the answer seems easy: if it’s winter, you take a winter sleeping bag. In reality however, it’s not so clear cut. For starters, winter is different in different parts of the world. Winter in the Mojave Desert is going to be different than Winter in British Columbia. (Heck, winter in Eastern BC is considerably different than winter on its West Coast.) Secondly, everybody is a unique sleeper. Some of us sleep particularly cold or warm. Some of us like to lay peacefully on our backs all night, while others like to curl up and spoon ourselves. The point is, good sleep in the backcountry is about having the gear that suits your style. Put another way, the right gear.

So let’s take a look at what you need to know regarding 3-season sleeping bags vs winter sleeping bags.

3-Season Sleeping Bags

3-Season Sleeping Bags

3-season sleeping bags are intended for use in—you guessed it—Spring, Summer and Fall. Because of the temperature variance that can occur over those three seasons the 20F/-6C is a very popular temperature rating for a 3-season sleeping bag. Versatile by design, a 3-season bag balances warmth and comfort with being light and compact so explorers can take advantage of all three of those seasons.

Here is our line of 3-Season Sleeping Bags:

Thermarest Winter Sleeping Bags

Winter Sleeping Bags

Winter sleeping bags are designed to keep you warm and comfy in sub-freezing temperatures. Heavier than 3-season bags, the extra bulk is absolutely worth it when the thermometer drops. The 0F/-18C is a kind of benchmark temperature rating for a winter sleeping bag. However, we all know that winter doesn’t stop getting cold when the thermometer hits zero. Winter bags come in sub-zero temperature ratings, like the Polar Ranger, to allow adventurers to experience even the coldest backcountry locations.

Here is our line of winter sleeping bags:

Sleeping Bag Temperature Chart

Understanding Temperature Ratings

The first thing to understand about the differences between a 3-season sleeping bag and a winter bag is their temperature ratings. Sleeping bags are temperature rated according to the EN/ISO Standards. The EN 13537 Standard was introduced in 2005 and the ISO Standard came along in 2017. Understanding these ratings allows consumers to make “like-for-like” comparisons of sleeping bags across brands.

You’ll notice that our winter sleeping bags have a maximum temperature rating of 0F/-18C and the 3-season bags have a max rating of 32F/0C. This is pretty typical for most manufacturers. For a winter bag, that rating means that 0F/-18C is the limit or transition range of the bag’s warmth capabilities. At Therm-a-Rest we have an onsite cold chamber so that we can flexibly test our designs throughout the development process. Many manufacturers have to send their prototypes off to a third-party facility for testing and rating.

According to the standard, in the transition range a typical sleeper, using just the rated sleeping bag for warmth (plus base layers), is “in a situation of fighting against cold (posture is curled up inside the sleeping bag), but in thermal equilibrium” and not shivering. It can be understood as the performance limit of your bag. Above the limit is the comfort range and below it is the risk range.

We choose to present these ranges—rather than just a single rating—to account for the individual differences between sleepers. With a range, our customers can make a more informed decision on which bag is right for them. If you’re a warm sleeper, perhaps you can comfortably use a 3-season sleeping bag for late Fall adventures when the weather is threatening winter conditions. If you’re a cold sleeper, you may want to consider bumping down to a winter sleeping bag for the same trip.

drinking warm drink in winter sleeping bag

Key Feature Differences

Why would you carry a 3-season sleeping bag if you might encounter wintry weather? Why not err on the side of caution and ensure you are warm with a winter bag? The most significant determining factor is the differences in weight and packability.

Weight & Packability

Winter bags are heavier and bulkier. That’s the most noticeable difference between a winter bag and a 3-season sleeping bag. Take for example our Questar line of bags, we have 3 season models and a winter model. The Questar 20F/-6C weighs 2 lbs 3 oz (990 g) whereas the 0F/-18C model weighs 2 lbs 11 oz (1,210 g).

8 oz (220 g) difference in weight may not seem like much, but it will definitely be felt as the trail miles add up. When you are carrying your gear under your own power into the backcountry you want to pack the lightest load that meets your performance needs. That’s efficiency.

In terms of sleeping bags, the lightest sleeping bag that keeps you warm and comfortable at night is the more efficient choice.

Insulation & Warmth

What accounts for the difference in weight and packability between a 3-season sleeping bag and winter bag? The primary factor is the amount of insulation in the bag. Which makes sense. Simply put, more insulation—whether it’s down or synthetic—means more warmth.

Each model in the Questar and Saros lines are essentially the same, but have varying amounts of insulation to achieve different temperature ratings.

airing out camp quilt

What About Quilts?

All of our quilts, by themselves, are considered 3-season quilts. The open-bottom design of a quilt limits its ability achieve the heat retention required for winter camping. However, quilts can be an incredibly valuable piece of winter gear when used as a layer.

Those of us involved in year around pursuits that need both 3-season and winter performance may opt to simply have multiple sleeping bags. The quiver strategy is a great one, but there is a slightly different way that offers more flexibility. Adding a quilt (or blanket) on top of your sleeping bag works the same as layering your clothes. You add warmth and lower the overall temperature rating.

Example: if you’re using a Parsec 20f/-6C 3-season sleeping bag, and you layer a Corus™ 32F/0C quilt on top, your new overall temperature rating would be about 5F/-15C. This is suitable for many winter pursuits. Moreover, in the summer, when the weather is warm enough, you can leave behind the bulk and weight of the Parsec 20F/-6C and use just the Corus 32F/0C. Which is more efficient!

The quilt is an incredibly versatile piece of gear that allows you to create an adaptable sleep system. Finer control of your system’s temperature rating allows you to dial it in right to your comfort preferences.

3 season sleep system

A Note on Sleep Systems

Whether you use a 3-season sleeping bag or a winter sleeping bag, it is only part of what creates overnight comfort and sleep performance. No sleeping bag is going to achieve its intended performance (read: keep you warm and comfy) without the proper sleeping pad beneath it.

Sleep systems are the sum total of the things you use to achieve good sleep. Pairing your 3-season sleeping bag or winter sleeping bag with a pad that has an appropriate R-Value for conditions will allow your sleeping bag to achieve its optimal performance.

There’s much to know about achieving overnight camp performance. We hope that this piece helped you become more knowledgeable and leads to better nights under the stars. If not, or if you have any questions, don’t hesitate to leave us a comment or reach out!

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