HOW TO CHOOSE... Sleeping Bags, Mats, and Liners

Date Posted: 7 December 2021

Choosing a sleeping bag can be a confusing and difficult process. We help you figure out which temperature rating, bag shape and loft rating is best for your purposes.

If you’re just starting out or looking to camp in a different climate than you’re used to, figuring out the correct sleeping bag to purchase is especially important.

Temperature Rating
When examining sleeping bag temperature ratings, keep in mind whether you sleep hot or cold. Not everyone sleeps the same; what one person might find warm might make you uncomfortably hot. Take note of whether you need a fan or air conditioning to sleep, or whether you consistently pile on blankets. As a general rule, women sleep colder than men. Sleeping bags labelled ‘Women’s’ are typically warmer and have higher down fills to make them reach their maximum warmth more quickly.

High-quality sleeping bags should always have an EN13537 rating. This is a European temperature rating system that accurately compares sleeping bags across varying manufacturers through standardised lab tests. EN13537 ratings provide three temperatures:

EN13537 Rating Example Sea to Summit

  • Comfort – the temperature at which a standard female can sleep comfortably in a relaxed position
  • Lower Limit – the temperature at which a standard male can sleep for eight hours in a curled position without waking
  • Extreme – the temperature at which a standard female can remain for six hours without risk of death from hypothermia (although frostbite is still possible)

Generally, when someone mentions a temperature rating for a sleeping bag, they are referring to the lower limit rating. If you are female or sleep cold, you may instead want to compare sleeping bags by comfort rating.

Environmental Factors
Where you sleep makes a big difference to whether you generate or lose warmth. Wind chill can affect you if you are sleeping under the stars or in a hammock.  A three-season tent limits wind chill and traps a small amount of your body heat. A four-season tent traps a pocket of warmth between the inner and outer layers, conserving your body heat more effectively.

Wearing layers, especially thermal underwear, also increases your warmth. 260g/m2 merino wool makes for the warmest thermal underwear, although thermals are available in a variety of fabrics.

The EN13537 rating system assumes you are sleeping in a three-season tent and wearing one layer of thermal underwear.

Sleeping Bag Shape
Sleeping bags come in different designs: mummy, rectangular, or tapered rectangular/relaxed mummy shapes are the most popular. Mummy bags generally have a higher temperature rating and are more expensive, since their more restrictive shape leaves a smaller amount of excess air inside the bag. Your body heat will warm up the smaller space much more quickly and result in an overall warmer sleeping bag.

If you like to move around in your sleeping bag, opt for a rectangular design with a slightly warmer temperature rating, to give yourself freedom but still stay warm.

A tapered rectangular or relaxed mummy fit sleeping bag is a compromise between the rectangular and mummy styles, and provides extra room for taller, broader sleepers. As with rectangular designs, you may need a warmer temperature rating in this style if there is excess space in the bag.

Some sleeping bags (including the BaseCamp, Trek and Voyager pictured below) can unzip all the way around to turn into a square blanket. These bags are great for warmer seasons, since one sleeping bag becomes a two-person blanket. Some other sleeping bags have a zip or drawcord at each end, so that you can poke your feet out while having most of the bag zipped up.

Sleeping Bag Shape Comparison

Loft Rating and Sleeping Bag Weight
A sleeping bag’s loft rating measures how well its filling (usually down) traps air. 550-650 loft is considered lower-quality, while 750 loft is good and 850+ is the best quality available.

Sleeping bags with higher-quality loft are NOT warmer. Warmth is provided solely by the EN13537 temperature rating. They are simply more compressible and lighter, since they need less down to reach the EN temperature rating. They will also take longer to 'puff up' to their maximum volume, meaning they can take longer to reach maximum warmth if you unpack them shortly before going to sleep. 

For maximum warmth, unpack your sleeping bag and give it a light shake as soon as possible when you make camp. The bag's temperature rating reflects its performance at full size, the more compressed it is from being inside the compression sack, the colder it will be. 

High-quality loft sleeping bags can be expensive. If weight-saving isn’t your top priority, you can cut costs by avoiding 850+ bags.

For backpackers and trekkers trying to keep their gear ultralight, however, a high-loft sleeping bag is a must. Some bags use a ¾ length or shorter zip to save on weight. Others use unique baffle constructions to optimise down density, resulting in the best warmth-to-weight ratios. Micro-weight shell and liner fabrics also cut down on weight.


Sleeping Mats
If your tent or sleeping bag is resting against cold ground, your body heat can be drained away into the earth. Sleeping mats offer a substantial layer between you and the ground, shielding your body heat from the cold and adding up to 6 degrees to the temperature rating of your sleeping bag. Insulated sleeping mats can further increase your warmth. And of course, they’ll provide extra cushioning for a smoother night’s sleep.

Sleeping mats are labelled with an R-value, which is a measure of their thermal resistance. The higher the R value, the more insulated the mat. As a rough guide, an R value below 3 is considered three-season camping; an R value above 3 is considered four-season. For seriously cold expeditions, you’ll need a 5+ rated mat. An uninsulated mat, while just as comfortable and cushioned, won’t be anywhere near as warm as the insulated version.


Sleeping Bag Liners
Sleeping bag liners increase the warmth of your bag and help to keep it clean. Many down bags are treated to be water-resistant. This is great during wet weather, but it can make cleaning your bag difficult since it won’t get wet easily. Sleeping bag liners will keep your sweat and grime away from the bag itself, and are usually machine-washable.

Purchasing a warm sleeping bag liner can also be cheaper than buying a bulkier winter sleeping bag, since you can simply add a liner to your summer sleeping bag for extra warmth. Check the listing when purchasing your liner to see about how many degrees it will add to your sleeping bag’s temperature rating. Try a Sea to Summit Cotton Travel Liner for comfort and hygiene, or a Thermolite Reactor fleece liner for maximum warmth.


We hope this guide has been useful to selecting your next sleeping bag. Armed with this knowledge, check out our current range of sleeping bags here. We also stock sleeping mats, liners and accessories to improve the warmth of your existing bag.

And as always, you’re welcome to contact us with any further questions. Happy camping!