How To Choose A Sleeping Bag

Now that summer seems to have arrived camping is most probably in mind. One of the most important and difficult buys needed for camping is your sleeping bag. With Mountain Equipment having revamped their range of down sleeping bags this year (click here to read the blog) and plenty of options from Rab, plus some specialist bags from OMM and Exped there’s a lot of choice. To help you out we’ve revamped our How to Choose a Sleeping Bag article.

A sleeping bag is a major purchase and your choice can mean the difference between a good night’s sleep and several hours of damp, cold misery or in extreme circumstances much worse. This means that when you come to decide on a bag it’s important to ask yourself as many questions as possible about just how you’ll use it. In this guide we’ll try to show some of the main considerations and highlight a few scenarios in which your choice of bag would be particularly important.

First ask yourself these questions:

  1. How cold is it likely to be where you’ll be using the bag and how much do you feel the cold?
  2. What conditions is the bag likely to face (weather, dirt)?
  3. How much space do you have for carrying the bag and how much weight do you want to carry?
  4. What is your budget for the bag?

Temperature Ratings

When it comes to sleeping bags the performance figures are always dominated by temperature ratings and inevitably the comparisons between manufacturers can be a little murky. The situation is further complicated by the fact that we all have slightly different insulation needs. I sleep fairly warm so I can often get away with a lighter bag where others will need four season insulation for the same conditions. The most important thing is to treat all the given figures as a guide. If you sleep warm then you’ll probably be comfortable in a bag somewhere below its comfort rating but if you sleep cold you might want a bag rated a little colder just in case. The extreme rating that you’ll see on most of our bags is intended to show the minimum temperature at which an experienced user could use the bag to stave off hypothermia: do not expect to sleep in the bag at this sort of temperature.

Some brands give their own temperature rating as they don’t think the standardised tests necessarily offer a fair reflection of the bag’s performance, particularly with higher spec, cold weather bags.

Here’s what Mountain Equipment say about their Good Night’s Sleep Guaranteed rating:

So confident are we that our sleeping bags will keep your warm and comfortable, in addition to the EN13537 laboratory ratings we quote, you will now see that every Mountain Equipment sleeping bag comes with a separate ‘A Good Night’s Sleep Guaranteed’ temperature rating. Resulting from a combination of scientific testing, countless field trials and exhaustive expedition testing, this temperature rating provides an indication as to the minimum temperature that we feel the bag should be comfortable to for an experienced user.

When thinking about the temperature rating of your bag you also want to consider 2 other factors:

  1. What you’ll be wearing inside the bag to sleep in. The temperature ratings on sleeping bags assume that you are dry, wearing full baselayer cover and have had a hot meal for tea. In fact exhaustion levels and your latest meal have a profound effect on how warm you are and have nothing to do with your bag.
  2. What you will be sleeping on. Thermal conductivity into the ground is the biggest cause of heat loss. If you are not currently warm enough then upgrading your sleeping mat may be a better space and cost solution than getting a heavier bag. A Foam or Down filled air mattress is far superior to a closed cell foam mat. Think of your bag and your mat as 2 parts of the same solution. You may wish to read our How to Pick the Right Sleeping Mat advice.

For all the geeky stuff on sleeping bag temperature ratings we have a separate article which goes in to more detail – Understanding Sleeping Bag Temperature Ratings.


One of the most important conditions to consider is how likely it is that the bag might get wet. For use biviing and open air camping or when you’ll be spending a number of days in wet climates it’s safe to assume that at some point your bag is likely to at least get damp. This is one of the most important questions to ask when you’re trying to decide between a synthetic and a down bag as down’s performance decreases severely when it gets wet whereas most synthetic insulation will shed water and even if it wets out will retain some insulating value.

One area where this is a particular concern is alpine bivis and emergency use. With the invention of hydrophobic down treatments (which pretty much all down bags now use) this is less of an issue with damp though there is a limit to how much it can do. Newer synthetics are also getting lighter and more packable it can be more efficient to pick a featherweight bivi, as opposed to a Gore-Tex or eVent one, and synthetic sleeping bag. Rab say this about their own hydrophobic down:

Here at Rab, we we protect our down with a Nikwax Hydrophobic Down™ treatment. Hydrophobic down will absorb far less moisture and dry far faster than other down. However, it is still unable to perform as well as synthetic alternatives in wet environments

Space and Weight

When it comes to pack size and weight, down is the king. Its remarkable ability to trap air means that for a given temperature rating you can expect a synthetic bag to weigh roughly 1/4 more and be 1/4 larger when packed. However for many camping situations – car camping, holiday use – these considerations may not be relevant. For backpacking think how big a sack you usually carry. If you like to pack light and carry a 30-40l pack for weekend trips then a bulky synthetic will be out of the question but if you’re prepared to carry a little more then you may think they’re the better choice. Here’s an example from Rab to illustrate the point:

If you compare two of our bags, the Neutrino Endurance 400 and the Summit 600 they both have a similar temperature rating, (-6°C and -6.5°C respectively), but the Neutrino Endurance is 285g lighter and packs down to 18 x 27cm rather than the 22 x 39cm of the Summit. Both bags will keep you warm, but if you’re travelling light or have limited space in your pack, then the Neutrino Endurance is clearly the better choice. The trade off is that the 800 fill power down used in the construction of the Neutrino Endurance 400 makes it considerably more expensive.

Ease of Care and Durability

Down sleeping bags require more care than synthetic bags. The feathers in a down bag are fairly fragile and will gradually lose their ability to loft over time. Occasional cleaning does restore the loft but this is best done by a professional service and the longer between cleaning the better. Synthetic bags are more hardy and can be machine washed at home without damaging the bag and so can be cleaned more often, however this is still best done as infrequently as possible. Neither type of bag likes to be stored long term packed tight in it’s stuff sack but this is more damaging to the loft ability of down feathers. So synthetic bags are better for dirty environments where regular cleaning will be necessary and will outlast a down bag. Tom Richardson, writing ‘Sleeping in the Mountains: 6 Tips’ for Mountain Equipment says:

Eventually it might need cleaning which should only ever be done by a specialist cleaner. Down works better when it is clean. Don’t do it yourself it will almost certainly be an expensive disaster – trust me.

Using a liner in your sleeping bag will significantly reduce the amount of cleaning it needs and therefore prolong the life and performance of the bag. A silk liner is not expensive and packs up to virtually nothing so it’s a complete no brainer.


One final distinguishing factor between down and synthetic fills is that the labour intensive process of producing, sorting and grading down means that it is more expensive than man made equivalent. A down bag can cost as much as Ł100 more than an equivalent synthetic. Plus, higher quality down (higher fill power) is more expensive than lower quality down.

So Which Bag Is For Me?

You can view all our sleeping bags here.

Choosing a bag is always going to be a compromise, no one bag can do it all. Here are some general starting points for various types of user:

Car camping and summer wild camping

For those who don’t camp that often and for whom weight is not such a concern, a synthetic bag represents excellent value for money. The addition of a silk liner will add versatility and warmth. The Mountain Equipment Starlight range is ideal.

General Backpacking and Summer Mountaineering Use

For most users who are interested in backpacking and mountaineering a midweight down bag is probably the best choice. This will be capable of everything from valley camping in mid-winter to long summer expeditions with only the very warmest and coldest days outside it’s comfort zone. Its usability can be further extended with a silk liner for insulation when it’s cold or to use on its own when it’s too warm. The Mountain Equipment Classic range is a good starting point. Hybrid bags, such as the Mountain Equipment Matrix range, and bags with tougher fabrics such as the Rab Neutrino Endurance range are also available.

Adventure Racer/Mountain Marathon/Solo camper/Ski Touring

For those who need the lightest and tiniest bags, Down is the usual way to go and the higher grade the down the less you’ll need to keep you warm. There are also some specialist synthetic bags available too. Have a look at the Mountain Equipment Fire range and the Rab Neutrino for down bags, for synthetic there’s the Mountain Equipment Aurora Range, OMM Raid and Exped Ultralites.

Alpine Bivi and Expedition Use

If you need low weight and pack-size but great performance and weather resistance then a high quality down bag with a more weather resistant outer shell is the best bet. The Rab Neutrino Endurance range is good for this and Mountain Equipment have the Fire range, the lower priced Helium range as well as larger expedition bags. The Mountain Equipment Aurora range is a good synthetic option.

For more information on Rab Sleeping Bags have a look at the Rab Guide to Sleeping Bags on their website.

Mountain Equipment have a similar article about their own bags on their site called Obsession Stitched In.

Click to view all our sleeping bags.

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