SLEEPING BAGS… Everything you ever wanted to know

Between you and a good night’s sleep are – howling winds, wheezing team mates, partying trekkers and rock covered tent sites to name a few – the last thing you need is a bad sleeping bag. A warm, well-fitting bag to snuggle into at the end of the day will dramatically increase your chances for a good night’s sleep.

Most people need a good night’s sleep. On the trail, this is particularly important because the body has been working extra hard during the day and needs time to rest and repair itself.

This information is to help you to choose the right sleeping bag for your individual needs.

Ask Yourself These Few Vital Questions…

  1. When will I use this sleeping bag most?
  2. What sort of night temperatures will I be experiencing most of the time?
  3. What do I sleep on?
  4. Will the climate be dry, wet or mixed, most of the time?
  5. Do I need a long or short bag?

When Will I Use My Sleeping Bag Most?

Here are some examples of the sort of questions you should ask yourself, with possible options for type of bag:

  • Am I going overnight camping? – Choose a Synthetic bag
  • Will I mostly use it for sleeping on peoples’ floors after parties and so need to wash it regularly? –  Choose a Synthetic bag
  • Will I be doing a lot of travelling, so bulk and weight is important? – Choose a Down bag
  • Do I regularly go cycle touring? – Choose a Down or Synthetic bag
  • Will I be at high altitudes and very cold conditions? – Choose a Down bag

If necessary, write down where you spend all your trips in one year and see what you are ACTUALLY doing for much of the time.

What Sort Of Temperatures Will I Experience?

Think in terms of the seasons of the year because this is exactly how manufacturers rate their bags.

  • One Season – for summer use with temperatures no lower than + 15°C
  • Two Season – for late Spring, Summer, Early Autumn use with temperatures between +15°C and + 5°C approx.
  • Three Season – for Spring, Summer, Autumn use with temperatures between +5°C and -5°C approx.
  • Four Season – for all year round use, but may be a bit warm for summer! Approximate temperature range is between -5°C and -15°C.
  • Five Season / Expedition – these are bags for extreme cold from -15°C to -20°C and below.

Deciding how warm the bag needs to be is a difficult task, but you know when you normally go out in the year, so select accordingly. Always be conservative and if you are caught between two season ratings always go for the warmer option especially with synthetic fills. Providing the bags have a full-length zip you can always cool yourself down, but it is difficult to make a bag warmer! Females are advised, unless you don’t feel the cold always choose a bag with a season rating one higher than is normal. This is because generally speaking women feel the cold more than men do. This is not sexist, simply learnt from experience!

What Do I Sleep On?

If the answer is not an insulated pad or similar, then be very careful. You get cold from underneath, not from the air temperature around you. Insulation from the ground is essential as sleeping bags offer little insulation underneath you. This is because your body weight crushes the filling and so stops it from ‘lofting’ or puffing up. So always, use some sort of insulating mat. Mats are either open or closed cell foam. The closed cell variety are resistant to compression, absorb very small amounts of water but cannot be reduced in size for packing. Open Cell foam is lighter, needs an airtight cover and tends to be self-inflating, these are heavier than closed cell mats, but are more comfortable, provide better insulation and some will pack down smaller. They are more expensive and if punctured have little insulation value. Conventional blow up air beds are impractical due to size and weight.

Will The Climate Be Dry, Wet Or Mixed?

This question can very quickly make the decision for you. If it is going to be cold and dry use down fills, or if cold and wet use synthetic fills and if the conditions are mixed, also use synthetic fills.

Down collapses when wet and loses all its heat, synthetic fills retain up to 60% even when wet. So, if there is a possibility of the bag getting wet always use synthetic. Unless you are like the mountain extremists who are operating in wet conditions but simply can’t afford the slight increase in bulk and weight of synthetic. Generally, this principle holds true for most non-specialist situations.

Do I Need A Small Or Large Bag?

Don’t get a bag where you only use half the available length because these won’t be as efficient in keeping you warm and you are paying for something you don’t need. The closer the bag fits to your body the warmer it will keep you. So long as it is not tight which crushes the loft. Baggy bags are cold as there is too much dead air, so get into the bag in the shop and check it out. Children can use an adult bag but use a cord to close off the bottom of the bag and tuck it under them for more insulation.

The Technical Stuff

By now you have chosen between down and synthetic fill, selected the right season rating for your use and so all you need is a few more technical details and you are ready to choose.

The Main Features of Sleeping Bags

Hood / Cowl

Hoods are essential in cold climates. They increase the comfort and warmth of the bag! For anything below freezing make sure your bag has one. A cold head can give you headaches and considerable loss of body heat.

Shoulder / Neck Collar

A lot of bags have a fitted collar to prevent hot air escaping. This is not restrictive but nice. Essential for really cold conditions, not necessary if it’s mild. Collars also work well for large people as they stop the bag riding down.

Zips

Essential for ventilation if you are using warm bags in warm conditions. In hot conditions completely unzip the bag and lay it over you like a Duvet or just lie on top. Make sure there are adequate baffles that run the entire length to prevent cold air getting in or warm air leaking out. Check the zip thoroughly in the shop before purchase. Always go for two-way zips if you can for greater flexibility. Two-way zips are often referred to a ‘foot friendly’ size as they allow you to unzip the bottom to air your feet.

Foot Box

The foot box is a specially cut and fitted panel in at the end of the bag which allows space for your feet especially in mummy bags. Without this your feet would compress the foot section of the fill reducing loft and making for a cold night.

Shapes or Types of Sleeping Bags

MUMMY: This is the best choice for weight conscious back packers. Mummy bags mirror the shape of your body – wide at the shoulders and tapered at the feet and head – without all that extra fabric causing bulk and weight. Their slim shape also means your body will have less space to heat up on a cold night.

COWL TOP: These can be either rectangular or semi rectangular. They have an integral cowl hood to keep your head warm. Mummy bags all have Cowls. Anyone going into cold weather should have a cowl. A large portion of your heat loss is through your head.

SEMI RECTANGULAR: This is the choice for people who need extra room to move around because these bags are slightly tapered at the foot, not totally form fitting. If it does not have a cowl to keep you head warm keep looking till you find a bag with a cowl.

RECTANGULAR: Rectangular bags give you the option of opening wide to use duvet style on summer nights. But they are not the best choice for trekkers. In cold weather, there is a lot of extra space to heat and all that extra material can be un-wieldy in your pack. Some rectangular bags have opposing zips so two can be zipped together to form a double bag with a close friend.

LINER BAGS: Insulated liner bags can add 70C of warmth to an existing bag, while washable cotton or silk liners will keep your bag clean after weeks on the trail.

BIVY BAG: Bivvies’ are un-insulated shells that minimalist’s use instead of using tents. Some feature mosquito netting over the face, others border on being one-person tents, with arched poles to keep the shell off your face and sleeping bag. Make sure any bivvy bag under consideration has factory sealed seams. Bivvies’ won’t keep you completely dry in serious rain but work fine otherwise.

OVERBAG: Over-bags are the way to go if you need to add up to 70C of warmth to your bag’s comfort range but your mummy fits too snugly to accommodate a liner on the inside.

CHILD’S BAG: A chilly child is the last thing you want, so using an adult sized bag is not the best idea. You can buy a child’s bag slightly too big so they will have room to grow, but don’t give their small bodies too much space to heat. Look for a mini mummy with a hood, and then hand it down when they have outgrown it.

Beware of cheap bags from large non-specialist chain stores – these bags are not suitable for serious walkers and only suit after party sleeping in your friends’ lounge.

Temperature Ratings

While the industry struggles with sleeping bag temperature ratings, we still have to rely on the individual manufacturers to provide their best guess. We all sleep at different temperatures, so manufacturers use their own general standard. The key is to just use the manufacturers labels as a starting point, factoring in the way you tend to sleep: warm or cold. If in doubt, choose conservatively and go with a bag rated 6 to 12 degrees colder than the temps you think you will encounter.

For most three-season use, a -50 bag is a good bet. For strictly summer or tropical use, +50 bags will serve you well. And for winter trips, look for bags that are rated -150 or colder. If you expect to spend lots of nights in a snow cave, then -300 bags are a minimum.

For most conditions, a four-season bag would fit into the following categories:

Synthetic fill:

  • A mummy bag with a minimum of 270g Hollofill per meter square.
  • A rectangular bag with a minimum of 300g per meter square.

Down fill:

  • A super down bag with a minimum of 280g per Meter Square. (+- 950g in whole bag)
  • A pure down bag (minimum of 80 % down cluster) with a minimum of 250g per Meter Square.

70% of the worlds down comes from China, although most of the finest quality down – 700 fill power – comes from Europe and Canada.

Shell Materials & Inner Linings

The sleeping bag shell is your first line of defence against condensation or spilled coffee, but it also needs to let perspiration vapour escape so the insulation material does not become soaked from the inside. Colour too can make a vast difference: darker fabrics dry faster in the sun.

Modern sleeping bags use ultra-light, windproof, filling proof and highly breathable fabrics in both shell and linings. The most common outer fabric cloths are plain weave nylon, Rip stop nylon or light micro fibres like Pertex. Lining fabrics also include Pertex and unlike early nylons, they are not sticky in warmer weather. Cotton and polyester mixes are still used as linings in some bags, and shops also sell removable cotton liners, in case you don’t like the feel of nylon next to the skin. In addition there are a whole range of other bag liners available, including silk, fleece and fibre pile. Whatever you do, always use a liner. If you want the best use silk, if you want warmth use fleece, (equivalent to one extra season) and if weight and drying aren’t a problem buy a cotton liner.

WATER RESISTANT BREATHABLE FABRICS: These water resistant fabrics block the wind and can add a few degrees of warmth to any bag. Micro-fibres and some proprietary fabrics are a bit more breathable so perspiration can pass through.

RIPSTOP NYLON: Rip stop is recognisable by its little checkerboard pattern. These lines of heavier thread make it more durable and abrasion resistant than plain nylons. Although strong and wind resistant for its weight, it is not water-resistant.

NYLON TAFFETA: Nylon taffeta is a flat woven fabric that provides a silky texture, but is not as robust as Rip stop nylon.

POLYESTER TAFFETA: Polyester taffeta stands up to the suns UV rays better than nylon taffeta and absorbs less water.

POLYESTER/COTTON: Bags with these shells may be cheaper, but they will not provide most trekkers with adequate protection. Any bag that contains even a hint of cotton will take forever to dry if it gets wet, even from perspiration, and will freeze up in cold, wet weather.

GORE-TEX: You will not find many Gore-Tex shelled sleeping bags anymore, because Gore has developed Dryloft, which works better with high loft insulation. You will find Gore-Tex in bivvy bags, though.

Inside Your Bag

A short guide to understanding your insulation.

Fill Material

This is the factor that most often causes sleeping bag shoppers concern. Down has a great cuddly feel and is lighter and warmer for the weight than synthetics, but some of the newer synthetics are close to meeting this standard. If you are the type who cannot seem to keep your sleeping bag dry, consider synthetics, as they dry faster and do not lose their insulation when wet. Canyoneerers should always choose a synthetic bag.

Down Filling

Natural insulation comes in the form of down clusters and feathers. Down traps heat very effectively, feathers by contrast are flat in shape and trap very little hot air. You can get either goose or duck down but there is very little difference for downs of equivalent fill power.

Soft down plumes underlies an adult birds’ outer feathers. Most sleeping bag down is a by-product of poultry raised for consumption, although most good manufacturers of quality bags import down specially bred for this purpose. Fill power refers to downs resiliency or loft; 550 fill

 

down is the basic, good quality variety. Most good quality bags these days have 650 or 750 fill, the fluffiest, lightest down available.

28 grams (one ounce) of down has over two million barbed filaments that interlock to create thousands upon thousands of dead air spaces to trap warmth.

 

A well-loved down bag will retain its loft up to three times longer than synthetics, but also requires more care, cleaning, and storage. Just don’t let your down bag get wet. They take weeks to dry properly and can cause the down to clump.

Down qualities vary enormously even to the extent that goose or duck down from one supplier is totally different than from another. The important criteria is the filling power of the down – what sort of loft the down gives for a certain weight. Although white down is generally more expensive than grey down it is not necessarily better. Eider down which is without doubt the best fill power down available is a dirty brown colour.

Pure Down and is made up of 85% down cluster and the balance is made up of down fibres. There are no chopped feathers used.

Super Down is a regional brand name for down which is not as good or pure as goose or duck down. It is far cheaper and as such has been made to a price. Some suppliers use a mixture of duck down & crushed feathers. Super Down is made of 55% down cluster and the balance is down fibre. There are no chopped feathers used.

Three quarter down means that the entire feather is used, which includes a portion of down at the end and half down, is similar except that the feather is longer.

Factors that determine the quality of down fill.

  • The first is the ratio of down to feathers. For a sleeping bag to be called a “down” bag, it must contain a minimum of 85% down. Many cheap bags use ‘chopped’ feathers which does not provide good insulation.
  • The second factor is something called “fill power” and is a simple method of measuring how many cubic inches a single ounce of down can occupy. The higher the fill power the higher the quality, the higher it will loft and the longer it will last. This is very important, because if one ounce of down fills 450 cubic inches and another fills 650 cubic inches, then the sleeping bag with the superior fill power will require less down to the fill the same space, as a result the sleeping bag will be lighter for the same warmth. It is this measurement of “quality of down” that can lead to such a difference in the pricing of bags that appear to have the same weight of fill. Bags can have anything between 450 and 800 fill power.

Facts about fill power

  • The higher the fill power the larger the down clusters – Longer lasting
  • The larger the down cluster the higher the quality – Longer lasting and warmer
  • The higher the quality the longer it will retain its loft and firmness – Value for money
  • The larger the down cluster the more mature the bird from which it came – Longer lasting
  • The larger the down cluster the more air it traps – Warmer
  • The larger the down cluster the higher it will loft – Warmer
  • The larger the down cluster the better the insulating power – Warmer
  • The larger the down cluster the lighter the down bag, will be – Less weight

700 fill power down is composed of 90% down clusters and 10% tiny feathers, and comes from 20 to 24 week old birds.

Synthetic Filling

Some synthetic fillings are warmer, some are lighter, some compress more, and some last longer, but all are less expensive than Down. Two main types of synthetic insulation exist; the first is made up of thin strands, or filaments, of polyester fibres, either continuous or chopped, which have one or more holes running through their length like a straw. It is these holes that trap the body’s heat, and the more holes the synthetic filament has, the more heat it will trap and the more effective it will be. The second, more modern approach is to batt (bond) micro fibres closely together, which trap heat between the fibres in much the same way that down does.

Short staple fibres like Lite-loft, Micro-loft and Prima-loft 1 and 2, pack relatively small and light. Polarguard bags made of continuous batts of fibre layered or quilted together, are a bit bulkier, but tend to retain their loft better over time. On the lower end of the performance spectrum are Hollofill and Quallofill bags that are warm enough and less expensive, but will take up more than their share of space in your pack. Pile or fleece bags make great warm weather bags that can also be used to supplement existing bags.

HOLLOFIL: This low priced polyester insulation comes in two variations. Hollofill II and Hollofill 808 which costs less. Both of these fills appear in entry level products.

LAMILITE: Is continuous filament polyester Fiberfil laminated to the outer shell fabric. It’s reasonably warm when wet. The continuous fibres take less layering to stabilise, saving weight and cost. Lamilite is slickened to improve stuffing and draping. The fibre structure resists the damages of wash and dry cycles better than most synthetics.

MICRO-LOFT: DuPont’s short staple polyester fill, made up of micro fine fibres thinner than a human hair. Its loft looks rather flat, but it is water-resistant.

POLARGUARD/POLARGUARD: Polarguard a continuous filament polyester, was one of the first lightweight Fiberfil’s. It’s still one of the longest-lived fills, although bulky to pack. Polarguard HV is a newer version with hollowed out fibres that are ostensibly 25% lighter.

PRIMALOFT: This short staple synthetic insulation is a combination of large and small diameter polyester fibres intermingled to create a down like feel. It has proved remarkably water resistant, making it a strong choice for wet weather trekkers. It doesn’t seem as puffy as other synthetic fills, but will keep you warmer than its loft will indicate.

QUALLOFILL: Even though the strands of this polyester fibrefill are slickened to regain loft quicker and drape around you better, Quallofill short fibres shed a lot faster than several other synthetic fibres. Newer generation products are replacing this material.

THINSULATE LITE LOFT: This premium synthetic fill is comprised of micro fine fibres heat bonded into a fluffy latticework. It is warm, soft and remarkably compressible but heat sensitive, so keep it away from heat.

MIRACLE FIBRE (Microfilament Polyester): These fibres are 1000 times’ smaller diameter than hollow fibre. This means that the fibres behave in a similar fashion to Down, trapping tiny pockets of air between the strands which is easily heated by your body heat, so, insulating you from the cold.

If you use the same sleeping bag more than fifteen nights a year, consider getting a liner. It’s easier to wash and dry than a bag, plus repeated washing shortens a bags lifespan.

Construction

Whatever type of filling you choose it needs to be held in place over and around the body. Synthetics are supplied in layers and so are easy to sew up. Either in a single layer (for summer use) or in a double offset layer (for year round use) or in shingles where batts of fibre are sewn to the outer lining and overlaid to eliminate cold spots. This is the most effective but also the most expensive method of construction for synthetic bags. Down is a free moving product, which must be blown into tubes or compartments of material. These tubes are then sewn together forming a series of channels.

It is the sewing of the fill to the outer/inner that poses the most problems for sleeping bag warmth. If the bag is sewn through, that is the three layers simply sewn all the way through, that means the fill is compressed by the sewing and allows the cold through. (In fact it’s allowing the warm air out) An easy trick is to feel the inside and outside stitching and see if they correspond. If they do it’s a problem, but if the stitching is off set, they its better. Most cheap bags are sewn through as this is a fast easy way of construction. Not good for cold climates.

Sleeping like a Log

How you use your sleeping bag affects how warm you will be.

  • Any bag straight out of the stuff bag won’t be as warm as it should be because the insulation is still partially compressed. As soon as you pitch the tent, un-stuff your bag, shake it out and let it regain full loft.
  • A sleeping mattress not only keeps rocks from your back, it keeps you warmer by cutting conductive heat loss underneath your bag. Forget the old five-tube airbed, and opt for a closed cell foam pad or self-inflating foam mattress.
  • “Warm when wet” is a distinctly relative term. Whether it’s filled with down or synthetics, any bag feels dreadful when wet. Keep it in a waterproof stuff sac, even a refuse bag will do. Maintain the outer shells water repellency with periodic spray moisture repellent touch ups. Be careful about keeping wet goods away from your bag.
  • Wet gear should be stored away from your bag. Condensation on tent walls can shower everything inside, so keep a vent open to minimise water build up. Air-dry your bag whenever possible, a sun warmed boulder is an ideal place to drape it.
  • In cold weather always wear a warm hat when sleeping, since much of your body heat escapes from a bare head. Wearing thermal underwear to bed often makes the difference between sleeping and shivering. Don’t overdo the added clothing though. If you overdress, the added bulk can compress the loft in your bag as well as prevent the heat from your body warming up the bag and you will sleep colder.
  • Food is fuel, so eat and drink warm foods before bedtime. The perfect excuse for high kilojoule bedtime snack.
  • Dehydration leaves you cold and listless so keep hydrated. Drink your fill before retiring, drink when you wake at night, and whenever else you can. You will know you are drinking enough when you urinate four or five times a day and it is relatively clear. Yellow urine is a sign of dehydration, unless you are taking vitamin B supplements which stain your urine yellow.
  • Since a bag cannot retain body heat that is not there in the first place. Eat a hot dinner and enjoy a hot drink before retiring. Just don’t go to bed sweaty.
  • Pour hot coffee, chocolate, or tea into you sleeping bag. By this we mean get into your bag then drink that last cup. In this way you are making sure you do not lose that precious heat to the air.

Goose down has essentially the same chemical make up as human hair. 88% protein, 11% nitrogen, 1% miscellaneous chemicals.

The Four Heat Thieves

If you slept through science at school, you will have missed the chapter about how and why you might wake up shivering in the middle of the night.

Here is a look at the mechanisms of heat loss in sleeping bags, and how a good bag prevents heat loss.

CONVECTION: The transfer of heat by moving air; for example, wind blowing through shell materials or zippers, or leaking around hoods. Convective heat loss is prevented by good bag detailing, like a snug hood and tight zipper baffles, windproof shell materials, and contoured mummy cuts.

CONDUCTION: transfer of heat directly through a substance, the way hot coffee in a cup warms your hands. Air is a poor conductor of heat so materials such as down or synthetics that trap lots of dead air (like body heat) in little pockets make the best insulators.

EVAPORATION: The loss of heat through the evaporation of perspiration. Your body loses heat through the night as you perspire normally, and as the sweat transfers into water vapour, large amounts of body heat are lost. Most sleeping bags do little to guard against evaporative heat loss unless they have a vapour barrier liner. (VBL). VBL’s are waterproof inner bag liners that harness the heat generated by the body through evaporation and prevent subsequent heat loss.

RADIATION: The transfer of heat between any two objects in direct line of sight or contact with each other. Stand next to a hot stove and you will feel radiant heat. Radiant heat loss in sleeping bags is solved through efficient insulators and bag construction that prevents cold spots. Some bags have special liners that reflect radiant heat back to your body.

Sleeping Bag Care

Although cleanliness is good, you should wash your bag as little as possible as the washing process reduces its efficiency. It is quite common for regular trekkers to have bags that are ten years old that have never been washed – just well looked after.

  • Do not roll your bag when putting it back in the stuff bag – it’s called a stuff bag for a reason – rolling creates folds at the same point all the time so damaging the fill – stuffing randomly folds the fill so reducing damage.
  • Cleaning any bag does effect performance to some degree
  • Avoid the necessity of cleaning by always using a liner
  • If cleaning always use natural soap products
  • Down is difficult to clean so use a recommended company to clean the bag
  • Always store your bag loose, either hung or rolled up loosely
  • Never store you bag in a compression bag for long periods – this will damage the fill.
  • Air your bag regularly when in use to prevent dampness
  • Always make great effort to keep the bag dry by:
    • Wrapping your bag in a waterproof cover inside your back pack
    • Choose your sleeping surface and location carefully
    • Checking your tent doesn’t leak
    • Not sleeping against the side of the tent or damp hut wall
    • In extreme conditions carrying the sleeping bag wrapped up inside your bivvy bag for full protection

The important lesson is to take precautions to keep you bag dry. Remember, dry bags are safe bags.

Final Bag Selection Checklist

The Basic Standard:

A -5°C bag is suitable for most three season trips. Down is a highly compressible insulation and provides more warmth for its weight than synthetic fills, which are preferable for use in wet conditions. Look for a zipper baffle, a draft collar and a trim fitting design for maximum heat retention. Condensation will dry faster on a dark coloured shell.

Variables:

Adjust the temperature rating up or down if you are a very cold or warm sleeper, or if your typical trip exposes you to hot desert temperatures or freezing mountain air. Some companies make bags especially shaped for the female form and for children.

Andrew Friedemann

Author: Andrew Friedemann

Andrew holds qualifications in South Africa, Australia and the UK as an Outdoor Recreation Instructor and qualified Mountain Guide and Instructor. Passionate about developing the Adventure Industry in South Africa to make it safer and provide opportunities to a younger generation of adventurers. Represented South Africa on the World Mountaineering Federations (UIAA) International Training Standards Commission for 10 years and has administered the South African Mountaineering Development & Training Trust. A qualified Wilderness EMT and Emergency Care Practitioner. Qualified as an Skills Development Practitioner, he has been intimately involved in the development of Adventure based qualifications particularly with regard the quality management of adventure qualifications. Founder of Adventure Qualifications Network, he was instrumental in the development of National Vocational qualifications for the adventure industry in South Africa, but also worked closely with Australia where he attained the Cert IV in Outdoor Recreation Instruction. Currently resident in the Scottish Highlands - UK, with his wife, Michelle, they travel to many areas of the world gaining information and skills. A keen adventurer, Andrew has participated in mountaineering, skydiving and scuba diving among other activities.

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