Sleeping Bags Guide
Sleeping Bags Guide
Sleeping bags come in a variety of shapes, sizes and materials and so choosing the right bag may sound simple, but it can be as complex as it is critical for your comfort, or even survival.
We hope that our Sleeping Bags Guide will help you know what to look for when choosing your next sleeping bag.
Sleeping Bags keep you warm by trapping and holding a layer of non-circulating air next to the body. This air, which is warmed by your body heat, forms a barrier between you and the colder air outside the bag.
However things aren't quite as simple as this, as technology has ensured that the outdoor enthusiast has a bewildering choice of bag design, fillers, ratings, shell materials and features.
Sleeping Bag Shape
In terms of shape, there are basically two styles of sleeping bag – mummy sleeping bags and envelope sleeping bags.
Envelope Sleeping Bags are rectangular in shape. They can usually be opened out fully and used as a quilt.
They are designed to be roomy but they do let a lot of body heat escape. Some models have hoods, but this is more for comfort (and somewhere to put a pillow) than to aid heat retention.
Because they open out fully, they are well suited to being zipped together to make a double sleeping bag.
The main advantages of this style of bag are that they tend to be more comfortable with a lot more legroom.
The disadvantages are that they are inefficient insulators and tend to be heavier and bulkier.
Because they are inefficient insulators, you are unlikely to find one rated as more than 2 to 3 season.
Mummy Sleeping Bags are narrow, close-fitting bags designed to save weight and maximize heat retention.
They start narrow at the feet, get wider toward the shoulder, and then taper to an insulated, fitted hood.
The majority of sleeping bags are mummy-shaped.
The slimness of the bag saves space and weight when carrying it and the hoods retain a lot of warmth in the body (one of the main places where body heat is lost is through the head).
However the narrow shape can feel prohibitive to some people and restrict their ability to sleep.
Sleeping Bag Fillings
There are two kinds of fillings used in sleeping bags - Down and Synthetic (although a few sleeping bags use a mixture of both).
Down is the thin, fluffy undercoating found just beneath the outer feathers of geese and ducks.
This natural fibre is a superb insulator. Goose down is preferred to down from ducks.
It is lightweight and fluffs up really well to trap air and is extremely compressible to pack away to a small size.
Down has excellent ‘drape’ properties, settling around the body and eliminating the draughty gaps sometimes left by stiffer synthetics.
It offers tremendous warmth for surprisingly little weight (thus offering a superior ‘warmth-to-weight’ ratio).
However, down is a poor performer when wet, taking much longer to dry. Also, down bags are expensive.
Although more expensive, remember that its resistance to deterioration makes it good value in the long term.
Down is graded according to fill power - meaning the number of cubic inches one ounce of down will displace. The higher the number, the better the insulation.
Synthetic fillings tend to be a bit heavier than down but are cheaper, easier to clean and have better performance in wet conditions.
Synthetic materials are basically plastic threads, normally a continuous long, single strand.
Usually the threads are hollow, reducing their weight and enabling them to trap more air, giving good insulating properties and reducing weight. Synthetic fillings dry fairly quickly and are non-allergenic.
The main disadvantage of synthetic fill is that the filling tends to be stiffer so does not drape over the body contours as effectively as down.
It is important to note that the weight of filling in a bag is not an accurate indicator of its thermal performance as the quality of fillings varies from manufacturer to manufacturer.
A high-quality filling may cost a bit more but gives better warmth to weight ratio.
Sleeping Bag Layers
Every sleeping bag has a shell (the outer layer) and a liner (the inner layer that touches the skin). In between is the filling or insulation.
In some bags, a metalised layer is integrated between the filling and shell to reflect back body heat. This can improve the performance of a bag by up to 15%.
The goal in bag construction is to avoid cold spots.
The insulating layer is held between the shell and the lining, and the even distribution of that insulation depends on how it is held in place.
Cold spots can occur where the stitching is used to hold the insulation in place.
Cheap sleeping bags represent low value because they are stitched through all three layers making a cold spot on every stitch line.
Quality sleeping bags prevent this by using baffles.
This means that the walls of the baffles are angled so each section partially overlaps the adjacent baffle.
With synthetic bags, sheets of insulation are offset-quilted and layered over one another to prevent cold spots.
Some synthetic bags are arranged with a Z-shaped system, which staggers how the insulation is arranged and assures that stitches on the shell (top) of the bag do not connect with stitches on the liner (inside).
Shell (or outer layer)
Shell Fabrics are also an extremely important part of the effectiveness of a sleeping bag. A close weave on the outer helps keeps water and wind out.
The most common fabric used today is lightweight nylon, which also offers low bulk.
Ripstop is often used on the outer because it incorporates a reinforced, fibre mesh to prevent tearing and, because of the increased strength gained, an even lighter material can be used.
Pertex uses many thousands of bundles of microfine yarn within its construction.
The capillaries created between these yarns actively draw moisture away from the source and spread it across the surface area allowing it to more readily evaporate.
As the moisture is evaporating from the fabric, and not from the occupant, chilling is dramatically reduced.
Lining (or inner layer)
Some bags use cotton as a lining, as this is very comfortable to sleep in. The penalties for using this are extra bulk and weight, and it is slower to dry.
The majority of bags use man-made materials for the lining, such as nylon and tactel nylon, or poly-cotton.
This is due to the superior wicking qualities of these fabrics helping to keep you dry, and therefore warmer.
When you buy a duvet or quilt, the manufacturer supplies a TOG rating for it.
Nearly all sleeping bags come with either a season rating or a temperature rating, or sometimes with both.
As stated earlier, do not rely on the weight of the filling.
For a full explanation of sleeping bag seasons and temperature ratings please see our Sleeping Bag Season Ratings Guide.
Remember that most sleeping bag ratings assume you will be using the sleeping bag in a good quality tent, that you will be using a sleep mat, and that you will be wearing warm night clothes.
This is a strip (or flap) of insulation that runs the full length of the zip.
It prevents draughts and heat loss through the zip.
If the bag hasn’t got a zip baffle it has probably been designed as a quilt that can double as a sleeping bag (e.g. for sleep-overs).
Warm air will always be able to escape from around the neck and shoulders, and a shoulder baffle will help to stop this.
Mummy style bags rated more than 1 season should always have a shoulder baffle.
Some mummy style bags will have a 3D footbox.
This gives a little more room for the feet making them more comfortable.
Some hikers put their shoes or boots in the footbox to prevent them getting cold and hard - if they need to be worn first thing in the morning they would be very uncomfortable.
Many sleeping bags designed for the military have a reinforced footbox, allowing the user to sleep with their boots on.
This can also be very useful for other outdoor activities like fishing and shooting.
Caring for your Sleeping Bag
There are some important things to remember in caring for and using a sleeping bag.
The sleeping bag should be fluffed up before use. This is especially critical for down bags.
This will restore the bag's full loft and thus make the most of its effectiveness.
Never leave a sleeping bag damp.
Dry the bag during and after every trip.
At home, stretch it out on a bed or floor in a dry room until it is dry.
In the field, it is best to avoid extended periods of direct sunlight (UV light is not healthy for fabrics.) The bag should be spread out on a dry, sun-exposed rock and occasionally moved to a different spot.
As it dries, fluff and bat the baffles to shake the filling out.
The bag should be stored in a cool, dry place (such as a wardrobe).
When not in use, it should be stored loose. Continual compression is bad for the filling (it will lose loft) and will reduce the life of your bag.
When using the compression sack, the bag should be 'stuffed' in.
Never fold it and roll it up to get it in.
This is because if it is folded and/or rolled, creases will tend to occur in the same place and cold spots will develop.
In conclusion, when evaluating different sleeping bags, it is important to consider these points:-
- Comfort/Season rating
- Insulation (down or synthetic fill)
- Weight & Size when compacted
- Personal sleeping habit (Are you a cold or warm sleeper?)
Always go for the best that you can afford.
A quality bag that is well cared for will be your best friend in any survival situation and will give years of service.
Remember that modern bags are much better than older bags that use old technology and always look for recommendations from people who have used them regularly in the worst of conditions.