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See also: Understanding Sleeping Bag Temperature Ratings.

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 other conditions is the bag likely to face?
  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.

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. You could be wearing more or less clothing than the assumed base layers and this change can stretch the usable temperature window of your bag.
  2. What you will be sleeping on. Thermal conductivity into the ground is your major source 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 way superior to a closed coll 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 more detailed information on understanding 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 it won't help if the bag gets properly wet (eg: in the rain or dropped in water). 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.

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.

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. 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 good for dirty environments where regular cleaning will be necessary and will outlast a down bag.


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 £100 more than an equivalent synthetic. This is further exacerbated by the fact that down requires specialist cleaning which can be costly.

So Which Bag Is For Me?

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 or Nova ranges are 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. Lighter bags such as the Rab Neutrino, and bags with tougher fabrics such as the Rab Neutrino Pro 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 Seat To Summit Spark ranges.

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 Pro 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.

And finally... If after considering all the above you're still unsure what to look for in a bag or you just need more advice then please call us and we'll be happy to offer you any help we can. Contact details just below in the page footer.