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Sleeping Bag Buying Guide

Buyers Guide to Sleeping Bags - Season Ratings to Insulation Types

Sleeping Bag Seasons Rating System

A sleeping bags performance level is generally measured by a 'Season Rating' system. This system is designed to give you an idea of the temperatures that the bag will perform best in.

Season Rating 1 2 3 4 5
Conditions Summer Spring / Summer Spring / Summer / Autumn Spring / Summer / Autumn / Winter Extreme (Expeditions)
Temperature Rating - Lowest Recommended 5°C 0°C -5°C -10°C -15°C

Be aware that there is currently no standard method for measuring the Temperature Rating of sleeping bags; this is left to the manufacturers discretion.

Obviously season temperatures fluctuate greatly from year to year and country to country so the above is for used as a guide only.

The above chart doesn't take into consideration variables such as: The use of any other thermal insulation, such as a rollmat, tent or any insulating clothing OR the type of activity you're doing (e.g. if you've been out in cold and wet conditions all day) - these factors will obviously have an effect on the type of bag you require.

Explore our range of 3 season and 4 season sleeping bags ideal for expeditions to see some examples.

Sleeping Bag Comfort / Extreme Ratings

When you are looking to purchase a sleeping bag, you'll notice that most bags have a recommended Comfort and Extreme rating, these are explained below.


Temperatures on sleeping bags are often shown as: Comfort: +20°C to +1°C.

This is the COMFORT temperature range - You should be comfortable in this sleeping bag between these two temperatures, anything above or below this range, and you may not get a good night's sleep, for example if the temperature fell below +1°C .

This can also be shown by some manufacturers as: Comfort: +1°C.

This is just showing the lowest temperature that you'll feel comfortable at. Anything less than this and you may feel the cold and wake up during the night.


Extreme temperatures are often displayed as: Extreme: -14°C

This is generally the lowest temperature you will be able to SURVIVE, at this temperature you risk injury from the cold, e.g. hypothermia.

Obviously these temperatures can only be used for guidance as comfortable sleeping temperatures vary from person to person depending on such factors as size and weight.

EN 13537 Temperature Ratings System...

EN 13537 (or EN13537) is a European standard designed to standardize the temperature ratings on sleeping bags manufactured and/or sold in Europe. It went into effect on January 1, 2005.

The standard measures four temperature ratings:

  • Upper Limit: The temperature at which a standard man can sleep without excessive perspiration. It is established with the hood and zippers open and with the arms outside of the bag.
  • Comfort: The temperature at which a standard woman can expect to sleep comfortably in a relaxed position.
  • Lower Limit: The temperature at which a standard man can sleep for eight hours in a curled position without waking.
  • Extreme: The minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia (though frostbite is still possible).
These may be displayed by manufacturers in a diagram such as: sleeping bag temperature rating EN13537

At temperatures in the yellow Comfort range, even inexperienced users will feel comfortable at all times. Users are likely to feel very cold at temperatures in the blue Risk range, with a risk of hypothermia. These midway values represent the lower comfort temperature limit for a male user. For females this is approx. 5°C higher.

For more information on COMFORT and EXTREME temperature ratings, download this booklet. (39 pages, A4)

Sleeping Bag Insulation Types

Blue rectangular down sleeping bag

Goose Down

Down offers excellent thermal properties, and has good lofting characteristics. This means that the down traps small pockets of air efficiently. The small pockets of air provide the thermal barrier. Down has the added property that it can be packed into a very small space.

For outdoor equipment, down is considered to be the single best insulating material available due to its light weight, compressibility, and heat retention. Take a look at our collection of down sleeping bags here.

Down insulation is rated by fill power, measured as the number of cubic inches displaced by a given ounce of down (in3/oz). Higher fill-power downs will thus insulate better than lower fill-power downs of the same weight. Insulation in most outdoor equipment ranges from about 400 to 900 in3/oz (230-520 cm3/g). Down rated 500-600 in3/oz (290-360 cm3/g) is warm enough and light enough for most conditions, and 800-900 in3/oz (460-520 cm3/g) fill is used for very lightweight and/or very cold-weather gear.

When wet the thermal properties of the down are virtually eliminated, making it a worse insulator than most equally wet synthetic fills. Compressed down is also a very poor insulator, and thus sleeping bags insulated with down require the use of a sleeping pad to provide insulation from warmth that would otherwise be conducted into the ground.

purple mummy shape synthetic sleeping bag

Synthetic Materials

The majority of sleeping bags are filled using synthetic materials for insulation. The most common synthetic threads are hollow, reducing weight and helping to trap more air.

Unlike Goose Down, synthetic materials retain a degree of their insulation power even when wet, dry relatively quickly and generally can be washed in a machine for convenience. Synthetic bags also have the advantage that allergic reactions are generally not an issue.

Something to consider when choosing between Down or a Synthetic bag: A synthetic bag with the same TEMPERATURE RATING as a Down bag will generally be HEAVIER and BULKIER. (Worth considering if you're backpacking and trying to keep bulk/weight to a minimum)

Things To Look Out For

Hoods: A hood can be a very useful addition to a sleeping bag as a lot of heat can be lost through the head on a cold night. Many hoods also offer draw cords so you can draw it in closer to your head, minimising heat loss.

Zips: As well as offering ease of access into your bag, zips can provide much needed ventilation on hot nights - Particularly useful for bags with a high temperature rating.

Baffle: A zip will create a cold-spot in your sleeping bag, allowing heat to escape. Zip baffles insulate the area around the zip, much like a storm-flap on a jacket will stop drafts from passing through.

Neck Baffle: Neck baffles can be found at the top of a sleeping bag - Fitted with a draw cord these can be tightened up to prevent any heat that your body has produced from escaping through the neck of the bag. A must-have for heat retention.

Compressions Bag: Most sleeping bags will come with a 'compression bag' which enables you to squash the bag up smaller than it would normally go, using compression straps. These can also be purchased separately.

Sleeping Bag Shapes

Rectangular bags: Less thermally efficient than a mummy shaped bag, but generally more comfortable - Great for family camping where heat retention and warmth are not a consideration.

Mummy bags: Mummy bags are far more thermally efficient than rectangular bags, fantastic for expeditions and adventures where warmth is a big factor. Mummy bags are generally lighter than rectangular bags as the close-fitment means that less material is required.

For Extra Comfort & Warmth

Bag Liners: add versatility to your sleeping bag and are a fantastic way of adding extra warmth, rather than upgrading to a brand new bag. Also by using a bag liner you eliminate the need to wash your sleeping bag after every use and can just wash the liner, saving time and prolonging the life of your bag. Liners are available in both Cotton and Silk versions for comfort.

Roll mat: A standard roll mat will provide a great deal of insulation from the ground when camping, as well as acting like a mattress and providing a soft area for you to lay on.

Therm-A-Rest (Self Inflating Mats): Therm-a-Rest self-inflating mats consist of an airtight nylon fabric envelope filled with a sheet of low density, open-cell polyurethane foam. When the valve is opened, air is drawn in, and the mat will expand to its normal size. When the mattress has fully inflated itself, the user simply closes the valve (to increase firmness, a few lungfuls of air can be blown into the mattress). To pack the mattress away after use, the valve is opened and the mat is rolled up tightly to force the air out, the valve is then closed to prevent re-inflation. There is a slight weight penalty in such mattresses compared to a roll mat, but this type of mat can provide isolation from cold and hard surfaces as well as a very comfortable night's sleep.


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