There’s nothing exciting abut sleeping bag temperature ratings, but it doesn’t mean they’re not important. Whilst you don’t want to be shivering, you equally want to avoid being too warm or carrying a sleeping bag that is too big and heavy for your trip.

There are various methods that help to determine the temperature ratings for a sleeping bag. However the Standard methods EN 13537 or ISO 23537 have now been adopted by the majority of sleeping bag manufacturers, including by Mountain Equipment. We played a large part in the development of this Standard and our staff continue to be part of the committee that works on its progression.

All of our sleeping bags display EN13537 / ISO23537 temperature ratings except our very warmest sleeping bags: our Extreme Expedition sleeping bags and Glacier Expedition bag fall outside the range of the test.

The EN/ISO tests produce three different temperature ratings:

Be honest: do you tend to car camp, backpack, or bivvy on ledges? If you mostly camp in places where the pack size and weight of your sleeping bag are not important, then consider buying a bigger, more spacious sleeping bag. But if you are alpine climbing or backpacking and carrying your sleeping bag for an extended period, then a lightweight sleeping bag is really important. Look for a sleeping bag that weighs under a kilo (2.2lbs) for a summer sleeping bag, and under 600g (1.3lbs) if you are really serious about shedding weight. If you are looking for a year-round sleeping bag that’s suitable for a variety of temperatures, then anything up to about 1.5kg (3.3lbs) will suit you perfectly.

The packed size of a Sleeping bag is closely allied to its weight, but there is also a huge difference between down and synthetic sleeping bags. A down sleeping bag with a Good Night’s Sleep rating of -20°C/-4°F may actually compress smaller than a synthetic sleeping bag with a temperature rating of -5°C/23°F!

Sleeping bags are either filled with down or with synthetic insulation. Down is warmer for its weight and packs smaller, so is a better choice for those who regularly carry their sleeping bag. Down is also longer-lasting and more comfortable to sleep in. However, synthetic sleeping bags are less expensive than down sleeping bags, they are more effective if the sleeping bag gets very wet, and they are easier to clean and launder. For most performance applications, down is superior to synthetic, but if you expect exceedingly wet conditions, then synthetic is the way to go.

The greatest factor determining how warm a down sleeping bag will be is the fill weight: how many grams of down are in the bag. The measure of the quality of that down is the fill power, with a greater number indicating greater quality. Roughly speaking, down above 700 fill power is very good down, down above 800 fill power is exceptional down. We use three different types of down in our sleeping bags:

Depending on the source birds, down may be grey or white in colour. Grey down is more common than white down and is sometimes regarded as less desirable because it may sometimes be seen through translucent or lightly coloured fabrics. However, colour has no bearing on the down’s thermal performance or cleanliness, and in the vast majority of products an end user will not even be aware of it.

Most of the down that we buy is grey. However, in some products with lightweight and lightly-coloured shell or lining fabrics we pay an additional premium for white down. White down is permitted to contain a small percentage of grey down or ‘black spots’, as obtaining a completely pure white down naturally is not practicable. These black spots do not affect performance and the down functions identically whether it is white or dark. As down moves inside baffles the position or even appearance of these spots is only ever temporary. It is possible to buy pure white down where there are no black spots, but this down has undergone an additional processing stage where it is sorted by hand. As a result, its price is much higher and it is available only in limited quantities.

Our down undergoes testing before it leaves our down supplier, once it reaches the garment or sleeping bag factory, and some final production garments are tested to ensure that the down meets the specification that we require.

Outer face fabrics are a sleeping bag’s first line of defence against moisture, snow, and spilt drinks. They stop insulation escaping the sleeping bag, but also allow perspiration out, and are an important factor in comfort. The table below summarises our various outer fabrics’ performances, with further details given below:

It's worth getting a bag that fits you. One that is too tight and restrictive will be uncomfortable if used for any length of time, while one that is too big can feel cold as the air inside may circulate freely.

Every Mountain Equipment Sleeping Bag is specified to one of five different fits: Expedition, Mountain, Alpine, Valley, and GT.

In turn, our sleeping bags are available in either Regular or Long lengths, and our women’s specific shape and specification in certain models. Women’s sleeping bags are shorter than the equivalent men’s sleeping bag by 15 cm/6 inches and also offer a marginally smaller footbox to suit smaller feet. They also come with EXL® stitching at the midriff which provides greater comfort, warmth, and an improved fit.

How a sleeping bag is constructed makes a big difference to durability, its ability to maintain warmth in wet conditions, and its weight. We use more complex construction methods than any other brand, but we do this because on longer or extreme trips, it really matters. It is also key to ensuring even warmth throughout a sleeping bag, as there is no point in having a warm torso if your feet and head are freezing.

Sleeping bag construction relates to how the insulation is held in place. For down sleeping bags that means how the baffles are constructed, and for synthetic sleeping bags it relates to how the sheets of insulation are sewn together.

You can find out more about the baffle type or construction type for each of our sleeping bags on their product pages.