Four Steps to Choosing a Sleeping Bag

Choosing a sleeping bag can be a daunting task. With so many different options and variations it can be difficult to get started. This will be one of the biggest investments, along with your tent, for backpacking so it's important that you make the right choice for what you need. We genuinely want you to pick the best sleeping bag for your adventures so we've put together this simple guide to help you narrow down the options for your search. 

Step 1 - Decide the temperature rating you need

You probably need to decide when you are most likely to go out and use your sleeping bag so you need to think about the temperatures you’re likely to encounter. The temperature a bag can be used down to, is often displayed with several ratings. To measure how low the temperatures can go before the user is uncomfortable, an international standard is usually used and this is the EN13537 rating. For information on the EN13537 rating you can read more here. This independent standard is used by nearly all reputable sleeping bag manufacturers and it produces two key ratings, the first is the 'Comfort Rating' which is the lowest outside air temperature at which a standard woman can sleep comfortably in the bag. The second rating is the 'Lower Comfort Limit' and is the lowest outside air temperature at which a standard man can sleep comfortably in the bag.

Both these ratings assume the sleeper is wearing a baselayer, hat, socks and using an insulating pad. In theory, men should be interested in the Lower Comfort Limit, and women the Comfort rating. However one component of being warm is our metabolism, some of us will 'sleep warm' and others will 'sleep cold' - a knowledge of our own tendency will also inform our decision. Therefore, if you are a man and the lowest temperature you expect to use the bag in is 0C then look for bags with a 0C Comfort Limit such as an ultralight bag that provides warmth utilising 900 fill-power down for example. If you are a cold sleeper you may want to go for a -2C or even -6C bag. Some people will be heading out in the middle of winter to experience the mountains where the conditions can be particularly harsh and a bag with a temperature rating of -20C or below may be required.

There are other factors that will affect how warm a bag we need such as... will you be in a two skin tent or single skin most of the time? Is it mainly for use in mountain huts or bivy bags? Will you be using a sleeping bag liner a lot? And crucially, how good is your sleeping mat? You can read more information on choosing the best sleeping mat for your sleep system here.

Step 2 - Decide on the type of filling you want - Down or Synthetic

The filling provides the insulation and stops you getting cold. Nearly all the bags we sell are filled with good quality 'down', this is because it beats any synthetic insulation hands down when it comes to keeping us warm for a given weight of filling and also packs down a lot smaller. Given the better performance of down sleeping bags versus synthetic equivalents why would anyone choose to buy a synthetic bag?

  • Initial cost - Down bags are much more expensive, although if looked after they tend to have a longer life.
  • Damp - Down is compromised when it gets wet - much more so than a synthetic filling, so a synthetic bag may be more suited to a wet environment.
  • Allergy - Down is a natural product and some people are allergic to it.

Most people will therefore choose to buy a Down filled bag. Down is graded into various qualities, referred to as the Fill Power, higher quality down is more effective at keeping you warm, and so you need less of it resulting in a lighter sleeping bag. One area to understand is that the more down you have in your bag the heavier it will be, but that doesn’t mean that it will be any warmer than a bag with less down of a higher quality. The higher the Fill Power the more effectively it traps heat so a bag with over 800FP down, will be warmer than one with 600FP down so it is important to think about the quality and the weight of the down combined.

Sleeping bag construction also plays a part in how effective the down is because if the down doesn't have space to expand into (or 'Loft') it will not be as effective. You could simply be guided by the EN ratings as to how effective a particular bag is, or you could look more deeply into it - for a fuller discussion of Down, Hydrophobic Down and Ethical Down you could read more here.

Synthetic insulation has improved dramatically in recent years from being heavy and bulky to very closely mimicking the attributes of down. There are a number of different synthetic insulation materials that aim to replicate down with many brands using their own materials developed with some of the leading insulation manufacturers. The main benefit of synthetic over down is its ability to retain warmth when moisture is involved. People using bivy bags for example, may opt for a synthetic bag due the issues around condensation

Step 3 - Decide what size and shape you need

The insulation in the bag keeps you warm by trapping a layer of still air around your body, thus reducing heat loss by Convection. In an effort to eliminate all possible space, choose a sleeping bag with an appropriate length for you. Therm-a-Rest bags come in three sizes: small (5 ft. 6 in.), regular (6 ft.), and long (6 ft. 6 in.). Pick the size closest to your measured height.

It is also easier to trap the warm air in if there is less volume of air to keep still, this explains the popularity of Mummy shaped bags which tend to be warmer for a given weight because there's less air to keep still, but that's no good if you feel restricted and can't sleep because of it. Larger bags or rectangular ones may be more comfortable for you and it may be worth the extra weight if it means you get a good night’s sleep. Step 3 is about deciding if you need the most efficient Mummy style bag or something larger that you feel more comfortable in.

However, you may simply wish for a more spacious, comfortable shape to your bag so you can move around more. If so, there are rectangular and semi-rectangular shaped bags. These shapes generally add weight and are not as focused on warmth so suit a more casual 2-3 season use for family camping trips or fair weather backpacking trips.

Another popular alternative is the use of a quilt instead of a traditional bag. With a lot less material needed there is an instant weight saving and in mild conditions you may not want the full body wrap style of a traditional sleeping bag. Paired with the right mat for insulation from below quilts can be used year round with a few adaptions to your system.

Step 4 - Decide which other features & construction methods are important for you

Once you have narrowed you’re your needs and wants from the first three steps shown, you may want to think about some of the finer points such as the specific design features included in the bag. Features may not make your sleeping bag warmer, but they may make it easier to get in and out of, easier to regulate temperature or protect you against draughts and moisture, all important considerations.

  • Zippers - long, short, on the side, on the top, around the foot.
  • Differential Fill - migration of down, backless sleeping bags.
  • Baffles - single zip, double zip, shoulder baffles.
  • Quilting methods - Stitch through, box wall, slant wall.
  • Vents - for dumping heat or allowing you to get your arms out.

There is more information on the options around zips, baffles and quilting methods for you to read here. There is also more to read on some of the other features and construction methods for sleeping bags here too.