Choosing and using sleeping bags, mats and accessories

cotswold camping
By Paul Deegan, Cotwold Outdoors, 04 April 2011
Nothing beats snuggling into a sleeping bag at the end of a long day in the outdoors. But all too often this simple pleasure is spoiled either because the bag has become damp from accumulated sweat, a tea spill, and moisture penetrating your rucksack, or because it has insufficient insulation to keep you warm. Whilst I’ve enjoyed luxurious nights in sub-zero conditions ensconced in sleeping bagscapable of fending off Antarctic-style temperatures, I have also been frozen to the bone in less extreme temperatures because I’ve been forced to use pathetically insulated (and occasionally soggy) sleeping bags. I hope that these notes will allow you to enjoy more of the former and less of the latter.

One of the first things to consider when choosing a sleeping bag is where and in what conditions you are going to use it. If the bag is only going to be used inside hostels or other sheltered and insulated accommodation, and if the bulk of the packed sleeping bag is not critical, then an inexpensive rectangular design with a L-shaped zip (which allows the bag to be thrown open quilt-style) will probably suffice.

At the other extreme, a mountaineer who needs the most heat-conserving type of sleeping bag will almost always opt for a snug-fitting sarcophagus design. This shape reduces the amount of dead air in the sleeping bag, and so provides maximum warmth albeit at the expense of some comfort.

Bags designed to be used in chilly temperatures will have features such as shoulder baffles, zip baffles, sculptured hoods, and also intricately designed foot sections which help to keep toes warm. The main features of a typical winter sleeping bag are illustrated below:
  • insulated full-length zip
  • multi-baffle hood
  • foot box
  • insulated shoulder collar
  • horizontal baffles over chest and body to stabilise insulation
  • tapering ‘mummy’ shape
Backpackers and trekkers sometimes opt for a tapered shape which offers some of the heatretaining benefits of a mummy bag whilst allowing a little more room for manoeuvre. Sleeping bags designed specifically for women are typically shorter in length than unisex models, with narrower shoulder areas and wider hip areas. They usually have extra insulation in the torso and footbox.

The filling used to insulate a sleeping bag needs to be held in place over and around the body. Synthetic insulation is usually supplied in batts and so is easy to sew up in a single layer (for summer use) or in a double, offset layer (for year-round use). Down, on the other hand, is a free-floating product that needs to be blown into cubes of material to stop it from shifting around and creating cold spots. This process is time-consuming and expensive compared to synthetic bag construction.

Understanding insulation
The main principle to bear in mind is that any sleeping bag is cold and useless until it is heated by a person. It is critical that you are generating heat and feeling warm when you get into your sleeping bag. If you wait until you are chilled to the bone before slipping into your bag then you’ll be in for an unpleasant surprise. Even if you are feeling toasty, a sleeping bag is likely to feel cold immediately upon entering it. But thrash around a little inside and the bag will soon warm up. The insulation in the sleeping bag traps your body heat and helps to prevent it escaping.
This filling will continue to keep you warm as you gradually cool down whilst lying still, and help to insulate you from the outside temperature, Of course, in sub-zero temperatures you’ll need more insulation than in the height of summer. When it comes to selecting a sleeping bag filling, your first decision will be to choose
between natural (down or feather) or synthetic (polyester filaments or fibre-pile) insulation. Which type of filling is most appropriate for your needs? Your decision will depend upon a number of factors including the weight you are prepared to carry, the amount of money you are able to invest, and in what conditions and temperatures you plan to use the bag.

Natural insulation
Natural insulation comes in the form of down kernels and feathers. Down is a superb
insulator. Kilo for kilo, these long-lasting tufts of fluff are the warmest and most
compressible filling that money can buy. Feathers, by contrast, trap very little heat. There is no world standard that determines what is pure down, down fibre, down feathers and pure feathers and so the down / feather ratio quoted by individual manufacturers is not always directly comparable. National standards vary considerably and this should be borne in mind when comparing bag specifications.

A more important consideration than the down and feather ratio is the strength of the down. This is measured by placing a specified amount of down in a container and measuring how much room it occupies under pressure. The result is known as fill power. Down with a fill power of 550 is often used in mid-price bags. Anything over 650 is excellent. A few topend bags have a fill power of 750 or higher.

A high fill power helps to reduce the weight of your sleeping bag. For example, if you
compared two sleeping bags with the same EN 13537 temperature ratings but with different strengths of down, the bag with the higher fill power would be lighter as less insulation would be needed to keep you warm at the stated temperature. Once again there is no world standard for fill power tests. Bear this in mind when comparing the specifications of sleeping bags from different manufacturers.

Down is not without its disadvantages. When wet it loses all its ability to trap body heat, and it can take many days to dry out. Down also needs to be looked after carefully.

Synthetic insulation
Most synthetic bags are filled with polyester filaments. These are designed to trap body heat just like down kernels without any of the natural fibre’s disadvantages. Many people opt for the convenience of a bag filled with synthetic insulation because it will typically retain up to half of its insulation value when wet. (In comparison, a wet down bag will retain less than 10 percent.) This makes a synthetic bag an appropriate choice for damp climates such as the UK and Patagonia, as well as perennially humid environments. A synthetic bag requires little attention when it comes to cleaning or drying out.

Generally speaking, a bag containing synthetic fibres needs more filling than a down bag with a decent fill power rating in order to perform effectively in a similar temperature range. So if low weight is your first priority then a down bag might be more suitable for your needs. A synthetic bag’s useful life is usually less than half that of a well-cared for down bag and prices are correspondingly lower.

Another type of synthetic bag is made from fibre-pile. Pile bags are usually covered with a windproof nylon shell. Fibre-pile bags have a very poor warmth to weight ratio when compared to synthetic filament and down bags. However, fibre-pile has the advantages of being incredibly durable and long-lasting. The material will also continue to trap heat very efficiently even when saturated. Pile dries out quickly, making it an excellent choice for mariners and military personnel.

Temperature ratings
Estimating how warm a sleeping bag is makes for a tricky business. After all, everyone feels the cold differently. Not only that, we all fluctuate in our resistance to the cold from day to day; energy levels, the state of our health and psychological factors all play their part. Age and gender also have an influence. Generally speaking, older people are more likely to feel the cold than younger people, and women tend to resist low temperatures less effectively than men.

All sleeping bags sold by Cotswold conform to a pan-European temperature test called EN 13537, which requires every bag to have four temperature ratings, the results of which are gained from a standard test. The four ratings are:
  • Upper limit: the highest temperature at which a typical adult man is deemed to be able to experience a comfortable night’s sleep without excessive sweating.
  • Comfort: the temperature at which a typical adult woman is deemed to be able toexperience a comfortable night’s sleep.
  • Comfort Lower: The lowest temperature at which a typical adult man is deemed to be able to experience a comfortable night’s sleep.
  • Extreme: a survival rating for a typical adult woman where there is a risk of hypothermia.The extreme rating should be treated with the utmost caution and never be relied upon for normal use.
Cotswold has taken the comfort lower ratings from the sleeping bags in its range and applied them to a season rating chart. This enables quick comparisons to be made between bags that have a similar level of performance.

Bear in mind that most season rating charts assume that you have recently enjoyed a hot meal and have retired to your tent wearing (when appropriate) a thin base layer, a hat, thin gloves, and a thin pair of socks. Your clothing and sleeping bag are dry, and you are lying on a sleeping mat.

If you know that you feel the cold, buy a bag in the next category up from your intended use. Sleeping bags can be uprated with a liner or outer bag if you occasionally find yourself heading for a destination that is slightly colder than your bag has a rating for.

Keeping your bag dry
Most types of sleeping bag fillings lose some or all of their insulating qualities when wet. However, moisture can enter the bag not only from outside in the form of rain, snow and tea spills but also from the inside via condensed sweat.

One tip for keeping your bag dry is to understand the dew point and how it can make your sleeping bag damp from within. The dew point is the point at which your sweat vapour condenses into a liquid. Normally this occurs outside the bag after your sweat vapour has passed through the insulation. However, if your sleeping bag lacks sufficient insulation to stave off the ambient temperature, the dew point can creep inside the filling. If this happens, the bag will start to become damp. In really low temperatures, your sweat can freeze inside the bag, forming ice crystals within the insulation. Placing an ultralight, oversized pile or synthetic bag around a down bag can help to prevent the dew point from moving into the down.

Regardless of the ambient temperature and the rating of your sleeping bag, some sweat vapour is likely to be left in the sleeping bag at the end of the night. Regular - preferably daily - airing is essential to maintain the thermal efficiency of the insulation.

In continuous deep cold temperatures in places such as Alaska and the polar regions, some people use an impervious vapour barrier (VB) liner inside their sleeping bags. A VB liner traps sweat vapour close to your body where it is held in suspension. This creates a warm and mildly humid environment. Sweat vapour is prevented from entering the bag and this helps to keep the insulation dry.

You breathe out a lot of vapour through your mouth. It is always preferable to sleep with your nose and mouth exposed, even if this means wearing a face mask or balaclava in cold weather. Also, keep a throughflow of air circulating in the tent, or you will end up with condensation dripping off the walls and roof of your tent.

Sleeping bags can get also get wet from river crossings, sodden clothing, rain and snow. When travelling, pack your sleeping bag in a waterproof liner, and avoid drying out damp clothes inside your sleeping bag at night. As for rain and snow, the first protection is either a decent tent or a bivi bag made from a waterproof and breathable material.

When it comes to preventing tea spills, invest in an inexpensive, insulated plastic mug with a lid. Try to keep liquids in the tent porch whenever possible. Some manufacturers employ water-resistant fabrics on the outside of their sleeping bags, enabling you to simply shake the worst of any spill from the bag as soon as any accident occurs. A small sponge is handy for mopping up any excess moisture.

Enjoying a better night’s sleep
Sleeping bags are not inherently warm, so it is important to get into your bag whilst you are giving off plenty of heat. In my experience, this is best done by consuming hot food or liquids whilst you are in the bag. At the same time, don’t drink too much liquid during the time before bed (unless you are at altitude where hydration is more important than sleep) or you may find yourself getting up several times in the night to relieve yourself. Drinking alcohol will force precious core heat to rush to the skin. Lowering your core temperature in this way can lead to hypothermia and so liquor is best avoided in cold climates.

At night you lose more heat through the ground via conduction than through the air. It is essential that you always lie on a foam mat (made from either closed cell foam or selfinflating open-cell foam) to replace the sleeping bag insulation you crush when you lie down. In addition, place any spare clothing between the mat and the sleeping bag to further increase warmth and comfort. In particularly cold temperatures fold your mat in half to double the insulation and place it under your torso. Put your legs and feet on top of your empty rucksack to help keep them warm. Some mats can be used in conjunction with chair kits to create a seat.

It’s easier to cool a warm body than heat a chilled one, so in cold weather utilise all the features of your bag as soon as you get in. For example, tighten the shoulder collar and hood drawstrings in order to create a heat-trapping seal around your face and neck.

Getting up in the middle of the night for a pee might seem like a quick way to get cold. But crossing your legs until morning is much worse as your body will have to divert precious heat to keep the urine in your bladder warm. Instead of being forced to exit the tent in the middle of the night, take a clearly labelled and leakproof 1 or 1.5 litre bottle to bed. (Women will find a funnel useful). In sub-zero conditions, either leave the full bottle in your bag (it’ll behave like a hot water bottle for a few hours) or reach outside and empty it immediately so that you don’t have to defrost a quantity of frozen yellow liquid in the morning.

If you are still not enjoying a better night’s sleep, it may be that your bag simply does not have sufficient insulation to keep you warm. If your sleeping bag is roomy, buy a thick fleece liner or a thin single season sleeping bag and slip it inside. This will help trap more heat and reduce the amount of air moving around in your bag which can cool you via a process called convection. If your bag is already fitting snugly, buy an oversized oneseason synthetic or fibre-pile bag and put your existing bag inside it.

Caring for your sleeping bag
Sleeping bags come supplied in tight-fitting stuff sacs. These should only be used during a trip when a small packed size is important. At home, store your bag in a large cotton sack, hang it in a cupboard, or lie it flat under a bed. Keeping the bag uncompressed will extend its useful life.

A dirty sleeping bag works less efficiently than a clean one. Avoid sleeping in the clothes you wear during the daytime as this only serves to drag dirt into the bag. Using a sleeping bag liner will go a long way towards keeping your bag as clean as possible. Cotton liners are cheap and cheerful but soak up sweat and can take a while to dry. Silk liners are more expensive, much lighter and dry more quickly than cotton. Fleece and fibre-pile liners are relatively bulky and heavy, and are best reserved for uprating the performance of your bag in cooler temperatures.

When your sleeping bag becomes a health hazard, follow the cleaning instructions closely as it is very easy to damage the insulation. Washing a sleeping bag takes time and effort, so choose a warm day well in advance of your next trip and follow the manufacturer’s instructions to the letter. Specialist down cleaning products are available.

Down bags are particularly troublesome to wash, and so many owners prefer to take
advantage of the services of a specialist who professionally wet cleans down bags. On no account have any type of sleeping bag dry-cleaned; the chemicals used in the process can damage the bag and the fumes given off are toxic.

Alternatively, some companies re-cover old down bags to give them a new lease of life. Or they will remove the existing cover, wash it, and re-fit it if yours is still in a good condition. This process avoids wetting the down. Extra grams of new down can be stuffed in at the same time if required. This can be a cost-effective way to uprate the performance of an existing sleeping bag. If you only have a few spots of grime that need removing, specialist sleeping bag shell spray cleaning products are available.

A specialist wet down cleaner recommended by some manufacturers of down equipment is: W. E. Franklin (tel: 0114 268 6161
Mountaineering Designs (tel: 015395 36333) will clean the shell of your old bag and add extra down if required.

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Paul is the author of the award-winning ‘The Mountain Traveller’s Handbook’, and is under licence to Cotswold Outdoor Ltd.

 © Paul Deegan under licence to Cotswold Outdoor Ltd.

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