Choosing the best sleeping bag for you

Choosing Your Sleeping Bag...

When selecting a sleeping bag there are a number of factors to consider before making your purchase. What temperature rating is most appropriate for your use? Are weight and pack size an issue for you? If you will be carrying your sleeping bag, pack size and weight will be more important. Would a Down or Synthetic sleeping bag be more appropriate? What is your budget?

Deciding how warm the sleeping bag should be.

The first task in selecting a sleeping bag is to decide which is the most appropriate temperature rating for your intended use. The details of the rating systems can be found in the Sleeping Bag Rating section. When making this assessment you need to take into account a number of factors. What time of year and where geographically are you going to be sleeping? - Obviously sea level summer camping will place less demand on your sleeping bag than winter camping at altitude. Which gender are you? - In general females tend to sleep cooler and feel the cold more than their male counterparts. Where are you going to be sleeping? - Rough under a tarp, in a tent or a cosy bothy? This will affect the ambient temperature around you and hence which bag would best match your needs. Do you feel the cold? - If you're a chilly mortal then consider purchasing a slightly warmer bag. If you only venture into cold conditions rarely would the addition of a fleece liner give you a more suitable solution for the vast majority of your trips? Is weight and pack size an issue? If you only camp from the back of a car then the pack size and weight becomes a secondary issue. If you're carrying your gear on a multi-day trip then you'll thank the day that you invested in some light weight equipment. For a given warmth rating, down will pack smaller and weigh less than its synthetic equivalent. We generally do not recommend fully compressing sleeping bags before placing them inside your rucksack, but to use a dry bag that allows the bag to conform around hard objects in your sack. This makes the rucksack more comfortable to carry, and actually uses "dead space" between rigid objects in your pack Is down for you?

Once you have decided on a temperature rating then the next major consideration is whether a down sleeping bag is suitable for the types of trip you will undertake, or would a synthetic fill be more appropriate. So next we will quickly outline the Pros and Cons of Down versus Synthetic insulation in sleeping bags.

Down Sleeping Bags
Down is a completely natural product. It comprises of the fluffy under feathers, generally termed down, from either ducks or geese. As a form of insulation, down is unrivalled in its performance despite recent improvements in performance of synthetic fibres. A down filled sleeping bag will be both lighter and pack smaller than its synthetic equivalent for a given application. If you need to carry your own equipment these advantages are often key.

Whilst the initial investment in a down sleeping bag is generally higher than for a synthetic equivalent, the expected life time is also considerably longer. Down maintains its ability to loft after compression much better than synthetic fibres. Typically with care a down sleeping bag will have a useful life in excess of twenty five years.

Synthetic Sleeping Bags
The main advantages of a synthetic filled sleeping bag are a lower purchase price and better performance if the bag gets wet. When down gets wet it tends to "clump" together and lose most of its insulating properties. Synthetic fills retain a great degree of their thermal performance and in general will also dry more quickly. Whilst the initial purchase price for a synthetic filled sleeping bag is lower, do not expect it to last as long. Depending on the care taken over storage, after 8 years or so, the synthetic fill will lose some of its loft and its performance will degrade.

Other considerations
Whilst at the budgeting phase you should also consider your sleeping mat. Sleeping mats not only provide comfort but also insulation from the ground. You will need to select an appropriate mat for the conditions you are likely to encounter. Given the insulation on the lower part of the sleeping bag is compressed under body weight and thus is far less effective, then the sleeping mat needs to compensate for the reduced performance in this area. Synthetic filled sleeping bags are not so easily compressed under body weight as down and will tend to retain more insulation under compression from your body.

As stated earlier in this article, down and wet conditions are not happy companions. Many Expedition rated sleeping bags have water resistant outer fabrics, designed primarily to shrug off the effects of snow. Waterproof sleeping bags, such as those from Exped, are available but at a price premium. Waterproof bags need to be breathable to allow the passage of water vapour due to perspiration. They also need to cope with the "dew point" being inside the bag in cold conditions so need to trap moisture and keep it away for the down itself.

One last intangible - the "drape" of a down sleeping bag tends to result in a more comfortable, snugger feel.

Hydrophobic Down
The latest development in the manufacture of down sleeping bags is the advent of hydrophobic down. The down is treated with a micro-polymer coating. This adds a small cost to each bag but potentially addresses the only weak spot in the down sleeping bags armoury. This technology is in its infancy but looks very exciting. The complete range of Rab® and Thermarest sleeping bags use Hydrophobic Down, using a fluorocarbon free coating developed in conjunction with Nikwax®.

Sleeping Bag Season Ratings

Traditionally Sleeping bags have been sold using the seasons rating system - all five of them!!! These are based on the typical temperature encountered in each banding at sea level in the UK. If you are going to altitude or to other regions you may need to adjust your choice.

1 Season
Designed for use in the summer only where the lowest temperature encountered is expected to be +5 °C or higher.

2 Season
With slightly more insulation, you should be comfortable from mid spring through to mid autumn. The lowest temperatures are expected to range between +5 °C and 0 °C.

3 Season
Spring, Summer and Autumn are covered by these sleeping bags although if it's a warm summer you may need to ventilate the bag. The Lower temperature range spans 0 °C down to -5 °C.

4 Season (or Winter Bags)
These sleeping bags are suitable for all year use including UK winters. As with the 3 season bags, you may need to unzip to increase ventilation in summer. The lower limit will be below -5 °C. Not really recommended for frequent summer use.

5 Season or Expedition
For extreme use at altitude or in Polar Regions. The lower limit will be much lower than -5 °C. These sleeping bags are designed for expedition use - they have a more robust construction, weather resistant outer shells and are generally sized to allow for additional layers of clothing to be worn whilst sleeping.

Temperature Ratings

As you browse through our website you will be aware of the various temperature ratings for each bag. The ratings will generally be based upon the European Standard EN13537, but where other systems are used the ratings will be clarified by the manufacturer's own sleep limit, e.g. the British Standard used for Criterion bags is shown as a Comfort Minimum. The same is true for the Rab Sleep Limit (See Below).

Today the generally accepted temperature rating system used for sleeping bags is based on the European Standard EN13537. However, this is not a compulsory standard so not all manufacturers comply. EN13537 results in four temperature ratings for each bag, although in practice the Upper Limit is rarely displayed.

The four temperature ratings are:

Upper Limit - This is the upper temperature at which a "standard man"* can sleep without excessive perspiration. This measurement is taken with zippers opened and arms outside of the bag. In practice this number is not always provided as you can always uncover more of your body to aid cooling.
Comfort Limit
- this is the lower temperature limit at which a "standard woman"* would be expected to have a comfortable nights' sleep in a relaxed sleeping position.
Lower Limit
- this is the lower temperature limit at which a "standard man"* would be expected to have a comfortable nights' sleep (8hours) in a relaxed sleeping position.
- finally this is the lower temperature at which a "standard woman"* would survive. After 6 hours there is a risk of hypothermia. Frostbite may still occur at this temperature.

* For the purpose of these measurements, a "standard man" is assumed to be 25 years old, with a height of 1.73 m and a weight of 73 kg; a "standard woman" is assumed to be 25 years old,
with a height of 1.60 m and a weight of 60 kg. The measurements are taken on a medium warmth sleeping mat. HOWEVER - These tests are undertaken in laboratory conditions so you will need to use a degree of common sense when interpreting these values. If you are a chilly individual then buy a warmer bag. If you are likely to be short of food, then you will sleep colder and will require a warmer bag. If your sleeping mat is thin, then again more insulation in the bag would be a good idea.

Criterion sleeping bags are not tested to EN13537. They are tested using British Standard BS4745 and ISO 5087-1 by Leeds University. The resultant TOG rating is converted into a temperature of each sleeping bag style. In practice this figure appears to fall somewhere between the EN13537 Upper and Lower Limits, so please take this into account when comparing sleeping bags rated using the different standards.

2012 saw the introduction of a revised version of EN13537 for sleeping bags. Rab have decided not to EN test their bags with fill weights of 800g and upwards. They feel that the revised EN test does not provide accurate results for bags operating at these lower temperatures. Instead Rab have provided a rating for these bags based on the EN 13537: 2002, the BS TOG results and real-life experience by their athletes and users - the value is know as the Rab Sleep Limit and this is the only value given for these bags.

Stitch (or Sewn) Through Construction

Stitch (or Sewn) Through Construction
This is the simplest construction technique employed in the production of down products. Cells are created by simply stitching through both the outer and inner fabric at regular intervals. This construction method is restricted to clothing and lightweight summer bags as the stitched area has virtually no insulating properties and results in cold spots. In addition, the cells have limited volume and restrict the amount of loft that can occur.

Box Wall Construction

Box Wall Construction
Thisis the original and simplest of the true baffle constructions. A perpendicular section of material spans the gap between the outer and inner of the bag. Box wall construction vastly reduces the cold spots compared to stitch-through, but the insulation level in the vicinity of the baffle is still slightly lower than the rest of the cell.

Slant Box Wall

Slant Box Wall
The next stage in development is the slant wall construction where the baffle is sewn at an angle. This lengthens the low insulation path adjacent to the baffle and gives a slightly warmer, if heavier
construction than a simple box wall.

Trapezoid Constuction

Trapezoid Constuction
This is probably the most popular construction method employed in higher end sleeping bags. It’s warmer than Box wall and lighter than V-baffle - a good middle ground, hence its popularity.

Construction Continued

Baffle Height
Baffle Height is the length of the baffle material between the inner and outer layers of the sleeping bag. Baffle height will vary according to the construction techniques used in the sleeping bag. This measurement will need to increase in proportion to both the fill power and fill weight of the down used in the bag to allow the down to fully loft.

Baffle height does not apply to Stitch Through construction.

Baffle Offset
Baffle Offset is defined as the difference in horizontal measurement between attachment points of the baffle to the inner and outer layers of fabric.

In cross section this resembles alternating sections of slices of pie. This approach gives the maximum number of baffles in a given length of all single layer construction techniques. The smaller baffles tend to give a more uniform distribution of down and so maximises warmth. The only drawback is the extra material does carry a small weight penalty.

Double Box Wall
With a cross section similar to a double skin brick wall this design virtually eliminates cold spots in the bag. This approach is generally used in high fill weight expedition bags. This approach is employed for the top half of the Cumulus Expedition sleeping bags.

Perpendicular Double Box Wall
This is the current pinnacle of down sleeping bag construction. In these bags the two layers of baffles are constructed perpendicular to one another.

Side Baffles
Taken as cross section through the middle of the bag, the baffles would appear as slightly off-set ovals. To discourage down migration from the top half of the cell to the bottom, side baffles may be employed. These can be a simple horizontal baffle, or of a more sophisticated design, similar to the V-baffle construction mentioned earlier. In general this approach is only adopted on warmer bags, such as those used for expeditions.

Zips and Zip Baffles
Zips are a thermal weak spot in the construction of a sleeping bag. Ideally they would be removed, but the reality is that they make using the bag much easier so are generally included in the design.

To minimise  the cold line of the zip most sleeping bags will have a baffle behind the zipper. For expedition use two overlapping baffles are used, attached to each half of the zipper.

Some sleeping bag models are available with either a left or right zip. This enables you to zip two sleeping bags together and does not necessarily have any bearing on whether you are right or left handed however, generally a right handed person would find it easier to operate a left zip from inside the sleeping bag and vice versa.

If your stature is on the large side or you anticipate the need to wear additional clothing inside the bag then additional Expander Baffles may be purchased. These are long wedge shaped down filled sections with a zipper on both long edges.They are attached to the two halves of the sleeping bag zipper to increase the internal girth of the bag.

Some sleeping bag models are available with either a left or right zip. This enables you to zip two sleeping bags together and does not necessarily bear any Hoods & Neck Baffles

Most of the sleeping bags that we sell are a mummy shape (as in Egyptian Mummy) i.e. included in the construction is a hood surrounding the head. As the temperatures fall, the need to insulate the head becomes increasingly important. The subtleties of the design of the hood can seriously impact the warmth rating of a bag.

Less obvious at first glance is the neck baffle. This is an internal tube of down that sits above the shoulders and around the neck. Its function is to restrict the expulsion of warm air trapped in the sleeping bag when you move about whilst you are sleeping.

Differential Cut and Differential Fill

Cut refers to the difference in circumference between the inner and outer layers of fabric of the sleeping bag. Stitch Through construction does not allow for a differential cut. With other construction types the differential cut allows the baffles to expand to the correct shape and
allow the down to fully loft.

Differential cut will vary according to the fill weight and fill power of the down used for a given bag. More down and/or higher fill power will require a greater differential cut as the volume occupied by the lofted down will increase both with fill power and fill weight.

Differential fill refers to the practice of selectively mapping the fill weight to differing cells created by the baffles within the sleeping bag. Certain Cumulus/Criterion sleeping bags bias the fill weights toward the upper half of the sleeping bag as the down crushed by body weight on the lower half of the bag has significantly less effect in keeping the user warm.

Foot Boxes
On simpler or older sleeping bags no allowance is made for the fact that feet sit at an angle to the lower leg. This means that the sleeping bag is crushed from the inside in the region of the toes. The result is a reduction in insulation and hence a cold spot about the feet. As a result most quality bags now have a shaped foot box, allowing room for the feet and stopping the internal crushing of the bag. Lady specific bags allow for the fact that women in general have poorer circulation and hence colder feet. On some bags more down is placed in this region, on others the foot box is fleece lined for a cosy feeling.

More Information about Baffles

Baffle Height
Baffle Height is the length of the baffle material between the inner and outer layers of the sleeping bag. Baffle height will vary according to the construction techniques used in the sleeping bag. This measurement will need to increase in proportion to both the fill power and fill weight of
the down used in the bag to allow the down to fully loft.

Baffle height does not apply to Stitch Through construction.

Baffle Offset
Baffle Offset is defined as the difference in horizontal measurement between attachment points of the baffle to the inner and outer layers of fabric.

Shape and Cut of Sleeping Bags
You will notice if you are comparing a wide range of sleeping bags that they vary in shape, sometimes in an obvious way and sometimes in more subtle ways. The shape of a sleeping bag will depend on a number of factors which may well conflict. The final shape of the bag will result
from the best compromises for it's intended use.

For best thermal performance and minimal weight then the sleeping bag needs to be close fitting. However this can result in a constricting design that feels very alien compared to sleeping in your household bed. For sleeping bags more typically used from the back of car at low altitude then a more spacious design, whilst less thermally and weight efficient, will allow a more "normal" sleeping experience.

Mummy Shaped
As used in the Rab Expedition and Andes sleeping bags. Fully enclosed hood and gently tapered shape that balances thermal efficiency and comfort in use. The Rab Expedition sleeping bags are oversized to allow for extra clothing to be worn inside the bag.

Mummy Taper Shape
The Rab Neutrino and Neutrino Endurance bags use this type of profile. Weight saving and thermal efficiency are paramount - to achieve this these bags are closer fitting, particularly around the lower leg region.

Semi Rectangular Mummy Shape
With a hooded upper section and a lower rectangular cut, bags this shape prioritise comfort over thermal efficiency. This shape is used on the Exped Versa range of sleeping bags.

Rectangular Shape
Typically used for buget bags, this shape is simply formed by folding a rectangular shape in half and adding a zip. Cheaper to produce, and closer in feel to being in your normal bed with a duvet, but also thermally inefficient. Currently we do not offer sleeping bags of this shape.

For lightweight applications in warmer climates one option is to use a technical blanket such as Thermarest Corus. Blankets have a more conventional feel and by removing the fabric and down from under your body can be very light weight.

Sleeping Bag Care

The following section covers maintenance and care of your down sleeping bag.

Day to Day Care
To prolong the life of your investment in a down sleeping bag there are a number of straight forward things that you can do: As the old adage goes “prevention is better than cure”. We would always recommend the use of a liner made from silk or a synthetic fabric; these are easily cleaned in the family washing machine and need no specialist treatment. External marks to your sleeping bag can usually be removed carefully with a damp cloth.

When not in use, store the sleeping bag in the storage sack provided. These are generally made from cotton or mesh and allow the bag to breathe and the down to loft. If your bag does not have a storage sack a large pillow case or a homemade sack constructed from an old net curtain will work

Always “air” your down sleeping bag (or synthetic) after a trip. A day or two left laying on a spare bed is ideal.

If away on a multiday trip then where possible, air your bag outside of the tent. Laying it across the top of the flysheet if it’s dry is the usual method.

Cleaning Down Sleeping Bags
If despite your best efforts, or after an extended period, a more thorough clean is required then you have two options: Cleaning at home Using a professional cleaning service

Cleaning at Home
Home cleaning should only be undertaken after fully assessing whether you have the skill and facilities to do so. As down tends to “clump” when wet, and because the fabrics used in the sleeping bags are delicate, it is easy to damage the internal baffles in the bag. If you are going to try home cleaning then we would recommend the use of a specialist cleaning product such as Nikwax Down Wash. The instructions provided by Nikwax are reproduced below. Please read thoroughly before starting: Use gloves. Use 150ml of Down Wash in 4cm depth of hand-hot water in a bathtub. Agitate to mix Immerse the sleeping bag in the hand-hot water in a bathtub. Agitate to mix, leave to soak for 5-10 minutes, then agitate thoroughly. Rinse clothing in cold water until water runs clear. For sleeping bags repeat process, drain and gently press bag to expel excess water. Sleeping bags can be transferred to a washing machine and spun slow twice, before a third or fourth fast spin. Drying of Down items should ideally be finished in a tumble drier... Spin dry 3 times (slow spin). If care label allows tumble dry according to manufacturer's instructions on a low setting until 'clumps' have disappeared. Shaking and patting the item regularly during drying process will help restore loft to the down. Never pack up a down item until it has been aired for at least a day after drying in a warm and dry space.

Including a clean tennis ball or two (check that they will not melt) in the tumble drier can help to break up any clumping of the down.

Professional cleaning
If you are not happy cleaning your down sleeping bag at home there are a number of specialists who will complete the task for you. We would caution against using local dry cleaners who generally, are not experienced in cleaning high quality, specialist sleeping bags. The following companies have the skill and knowledge to clean your down sleeping bag correctly:

• W L Franklin (Sheffield) 01142 686 161
• Mountaineering Designs (Kendal) 01539 536333

What do all these terms mean?
There are a number of parameters that are associated with down sleeping bags, an understanding of which will make it easier for you to compare various models.

Fill Power
This is a way of assessing the quality of the down used in the construction of the bag. It gives the volume (in cubic inches) to which an ounce of down will loft (expand) to occupy. The higher the number the better the quality of down and hence the warmer the sleeping bag will be for a
given weight. The industry seems to be migrating towards using US fill power ratings. More economical bags will generally use 650 FP down, high end bags will typically use 800 or even 850 FP down.

Fill Weight
This refers to the weight of down (in grammes) contained in the sleeping bag, i.e. a 900 fill weight bag will contain 900 grams of down.

Down / Feather Ratio
All down sleeping bags actually contain a mixture of feature and down. The two parts tend to perform differing functions within the sleeping bag. The down is primarily responsible for the insulating properties of the fill, whilst the feathers help the fill loft fully within the compartments in the sleeping bag. Typically this figure might be a expressed as 94/6, indicating the 94% of the fill is down and the remaining 6% is feather. Higher down ratios are more expensive as down costs more than feather to produce. The ratio will only ever be approximate as the categorisation of down versus feather is subjective and so dependent upon the individual doing the sorting.

Want to know more about Rab Down Sleeping Bag construction and ratings, then click the Rab logo?

Want to know more about Rab Down Sleeping Bag construction and ratings, then click the Rab logo?

Want to know more about Criterion Sleeping Bag construction and ratings then click the Criteron logo?
Want to know more about Criterion Sleeping Bag construction and ratings then click the Criteron logo?

Please note that Cumulus UK is currently being re-branded as Criterion.


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