Understanding your sleeping bag properly
Individual temperature sensitivity: everybody feels the cold differently
Buying a sleeping bag is a highly individual decision – the decision depends on how you intend to use it, your own personal feeling of warmth and physical constitution. Just because a certain sleeping bag “works” well for a friend, it does not necessarily follow that it will be the same for you...
The reason for that is simple: each person has a different, highly individual feeling of warmth. Therefore any ‘official’ temperature specifications (such as those defined by European standard EN 23537) can only serve as guide values.
How does a sleeping bag keep you warm?
A sleeping bag does not give off its own heat, but, thanks to its insulating properties, retains the body heat you give off. The more air a sleeping bag stores and the less air circulates in the sleeping bag, the more effectively it works.
Heat loss in a sleeping bag
There are several reasons for heat loss when you are sleeping in a sleeping bag:
- Convection (air exchange): Air circulation leads to heat loss, for example when the zip is open or due to the draught collar not being there or not being used below zero degrees, because the warm air from the sleeping bag mixes with the cold ambient air. As a result, the body constantly needs to produce more energy to maintain a constant temperature in the sleeping bag. This also applies if the sleeping bag is too large or too small.
- Radiation: Our body radiates warmth. The better a sleeping bag reflects and stores this heat, the less energy the body needs to generate to achieve a constant temperature in the sleeping bag.
- Evaporation: Everyone gives off about ½ litre of moisture through the skin through the night. If moisture remains on the skin, cold evaporation develops and the body tries to dry the skin using heat. The drier a sleeping bag keeps the skin, the more energy the body saves.
- Conduction (heat conduction): The less insulating properties a material has, the faster heat dissipates, for example in direct contact with a cold floor.
A good sleeping bag should keep heat loss as low as possible. The materials used, the construction and shape of the sleeping bag all have a direct influence on its insulation capacity.
Comparable temperature indications
The uniform test procedure defined by the European standard 'EN 23537' guarantees an unbiased comparison of sleeping bag temperature indications.
Here is a detailed explanation of the temperature indications and the test procedure.
Materials for the sleeping bag filling
There are many ways to achieve good insulation. Down or synthetic fibre sleeping bags as well as wool sleeping bags have firmly established themselves in today’s ”outdoor world”. Which sleeping bag made of which material is suitable for which use depends mainly on the area of use and is a product of the following material properties:
Synthetic fibre in your sleeping bag – the easy-care product
The raw material polyester as a filling material
The raw material for synthetic fibre filling is usually polyester, which is processed into fine fibres. A fibre consists of several filaments.
A distinction is made between staple fibres and continuous filaments.
Staple fibres are cut and “glued”, which is done thermally or using actual adhesives. Their construction makes these filling materials fluffier and softer to the touch. These fibres sometimes require an additional fleece depending on the fabric construction. The thickness of the insulation is very even. If they are designed to be water-repellent, they “swim” on water.
Continuous fibres are extremely tear-resistant and generally more stable. However, they tend to be somewhat “heavier”. This means that slightly less fibre-dense outer fabrics can be used. A typical example of this type is Polarguard. There is no need to sew in extra fleeces.
Various shapes of synthetic fibre filaments
These filaments can be geometrically constructed into different groups. Some of them are hollow, hence the name hollow fibres. Their hollow chambers are round, star-shaped or triangular. Some manufacturers bundle several hollow fibres into one another. The three-dimensional shapes of the filaments or crimped structures provide more stability and offer more bulk to the filling.
Type of filling
Synthetic fibre fillings can be incorporated into a sleeping bag in different variations.
Much like down filling, the synthetic fibre filling material is blown loosely into individual chambers of the sleeping bag cover. This results in a very high loft, but the filling can slip and, depending on the chamber construction, create cold bridges.
Very often synthetic fibre fillings are processed in the form of a mat/fleece. This enables an even thickness of the filling material, which then cannot slip. Furthermore, a construction can be made with very few seams/cold bridges.
Fibres often receive further treatment to give them special features. This is called its “equipment”. Silicone coating makes the fibres more supple and thus more resistant to shear forces that could otherwise break the fibres. Other finishes also make the polyester filling itself water-repellent.
Advantages of synthetic fibre fillings
The fineness of the fibre and the three-dimensional structure, achieved by its construction and fibre bonding (example: air textured) and/or staple technology, keeps the air enclosed, reduces air circulation and thus increases the insulation effect. This remains largely unchanged even in “normally moist” conditions. Other advantages are the relatively low price of synthetic fibre sleeping bags, their robustness and low care requirements.
Disadvantages of synthetic fibre fillings
Synthetic sleeping bags can become relatively heavy when required for lower temperatures. A synthetic sleeping bag cannot be compressed as much as its down counterpart. After having being compressed, the filling also needs more time to regain full loft. The biggest disadvantage is the uncomfortable sleeping climate, as synthetic fibres are very limited in their regulation of temperature and humidity.
Synthetic fibres are sensitive to:
- being constantly rolled and packed in the same way, as they thin out and become weaker at the highly stressed areas.
- Too high machine wash and tumble dryer temperatures, as the adhesives become unstuck!
- Incorrect storage (compressed in a transport bag).
- Tensile load (packing or twisting of sleeping bag).
- They cannot develop as good a climate as natural fibres.
Down – sleeping on feathers
Down is a natural product. It has an excellent thermal insulation to weight ratio. Compared to synthetic fibres, the sleeping climate is more comfortable (but only when used in combination with breathable inner and outer fabrics!). It can also be extremely heavily compressed over a short period of time without losing its properties. The resulting packing volume and the above-mentioned ratio of insulation to weight make them particularly beneficial for Alpine use.
Down and feathers – what is what?
Down – the so-called “down ball”, a point-shaped core with three-dimensional branches – is never used alone, but always together with support feathers. These form a stable “elastic” matrix where the down can unfold. This is combined in a mix ratio, e.g. 80% down, 20% feathers. The ratio is determined according to the area of use and price-performance ratio. Many people forget that the quality of the feathers is almost as important as that of the down. For example, if the feathers are brittle and the quills are splintered, the sharp keel shards cut open the fabric and the seams. There are between 500,000 and 1,000,000 down feathers to every 1 kg of down.
Mixing ratios down / feathers:
- 50% : 50% = bed linen, cheap sleeping bags. Weight is not a relevant factor. Less insulation.
- 60% : 40% = camping beginners. Cheap sleeping bags.
- 70% : 30% = good camping sleeping bags. Robust construction, partly duck down.
- 80% : 20% = Alpine beginner models, more expensive models. Better weight / insulation ratio. Almost completely goose down.
- 90% : 10% = top – Alpine sleeping bags. Expensive. Need more intensive care. Very good weight/insulation ratio. Goose down.
High bulkiness or fill power
The bulkiness of the down is specified in CUIN. Fill power is a characteristic measure for down and other upholstery fabrics, which indicates the volume a certain mass of the fabric takes up again after some time of compression.
Standardised test procedure for the determination of the fill power
A commercially available unit is cubic inches per ounce (in ³/oz or cuin for cubic inches). The US Standard 2000, for example, measures in a glass cylinder with a diameter of 241 mm (compression 68.3 g) by compressing one ounce (≈ 28 g) of the down mixture in the measuring cylinder for 24 hours. Then the volume to which the sample expands is measured and expressed in inches (1 inch³ ≈ 16.4 cm³).
The European and American standards differ slightly, but the results are comparable (EN 284 mm DM, 94.25 g mass. Down weight 30g – IDFB testing regulations).
The higher the fill power value, the better the thermal insulation in relation to the packing volume. The fill power is one quality standard, but not the only one.
Cuin values in practice
- 400 – 500 cuin are good and sufficient for many applications such as bed linen.
- 500 – 600 cuin represents a good value, duck down has its limit here. Models with 600 cuin are considerably more expensive.
- A high-quality down sleeping bag should have 600 -700 cuin. However, a little more care is required here.
- 700 – 750 cuin is a top-of-the range product.
- More than 800 cuin or even above is very rare. (But this can be achieved by strong cleaning. This causes the down to lose its protective layer of fat and makes it more sensitive to moisture)
Further quality indicators with down
The purity (after washing and preparation) of the down is indicated by the oxygen number. A higher number indicates organic residues, possibly even bacteria. 1.6 to 3.2 are very good values. The highest value that can still be tolerated is 10.
Other values are the turbidity number, the oil-fat content and the pH value. These values do not usually appear in the descriptions, as they can change depending on the user and washing behaviour.
Origin and species
The origin of the down also plays a role. Goose down is usually larger than duck down, with the result that its three-dimensional structure is larger. If the animals come from colder regions, the structure is also denser compared to animals from more southern regions.
Down and moisture
Objectively speaking, down is fundamentally very robust – and this also goes for moisture. However, it loses this property somewhat during cleaning and the manufacturing process into sleeping bag down. This means that down is much more susceptible to moisture than synthetic fibres. In certain situations, if they absorb more moisture and clump together, they may no longer generate any volume. The result is reduced insulation capacity.
A down sleeping bag must therefore be ventilated as often as possible and, in extreme cases, dried.
Problems often arise with down sleeping bags in winter or permanent frost regions. Evaporation from the body is stored by the down and freezes there. It is very difficult to dry it. After a while the down clumps together and loses its insulation capacity. The problem can be reduced by choosing suitable functional underwear.
Down and chambers
In order to prevent the filling from slipping, the “loose” down is filled into chambers. Cheap quilted chamber seams form cold bridges. Good sleeping bags have sloping chambers, trapezoidal chambers or “H-chambers”.
The arrangement, elasticity and choice of material play a role as well as the shape of the chambers. Elastic chambers prevent the seams suffering excessive force so that they do not widen and let the down “slip through”. If the chambers form a ring around the sleeping bag, you can shake the down more towards the front or on the back as needed and thus customise the sleeping bag to the current temperatures.
Down sleeping bags are therefore particularly suitable for excursions which call for small packing dimensions and weight combined with optimum insulation (e.g. mountain trips).
In principle, down is less sensitive to being packed than synthetic fibres. Nevertheless, a down sleeping bag should be kept dry and airy in a slightly larger, air-permeable storage bag.
Down should be washed with a special moisturising detergent to keep the down supple. Down sleeping bags are very durable when stored appropriately, even more durable than synthetic fibre sleeping bags. You can find detailed washing instructions here.
Wool – the height of sleeping climate control
The development of a sleeping climatic miracle worker
If you have ever camped, trekked or slept in a sleeping bag, you will probably be only too aware of the dampness and cold when you awake the next morning. The body releases moisture (up to 500 ml per night) and the dew adds the rest.
This moist, cool combination means the body needs to use a lot of energy to regulate its temperature. That means that you don’t sleep particularly well and don’t wake up feeling fit, and often even with back pain, because the muscles cool down due to the moisture.
This is exactly what troubled Markus Wiesböck, the founder of Grüezi bag. He wanted to sleep well on holiday, wake up fit and be fully refreshed to enjoy the day’s experiences.
In his 30 years of experience with sleeping bags, their development always revolved around making them even lighter, and the effect on Markus was that he slept worse and worse as a result.
That led him to start experimenting with different materials. After a seemingly infinite number of tests with synthetic fibre, down, kapok (nature’s finest vegetable hollow fibre from the kapok tree), beech, alpaca, camel hair, new wool and much more, he finally got the result he had been searching for: a good nights sleep. And this with a material that has been used for thousands of years, just never in your sleeping bag.
Alpine wool acts as a natural air conditioning system
The Alpine wool used in sleeping bags serves as a natural air conditioning system: the body releases moisture all the time. However, if there is too much humidity in the sleeping bag, the body gets cold and you do not get a good night’s sleep. Wool absorbs moisture and passes it on to the outside in doses to prevent cooling by evaporation. This regulation by the wool provides both a warming and cooling effect and creates a balanced sleeping climate in the sleeping bag. The resulting feel-good experience ensures a relaxed night’s sleep. Wool warms even when wet. It can absorb up to 30% of its own weight in moisture while still retaining its insulating properties.
Grüezi bag uses wool from Alpine sheep as filling for its Biopod product line. This is supplied by the well-known wool supplier Lavalan. PLA (corn starch) is added to the wool to make the alpine wool washable and even more stable. This prevents the wool from slipping around, makes it washable and even more easy to dry.
Wool and sleep research
Studies such as Woolmark Australia show that you sleep longer and more restfully with wool. The best skin temperature for sleep is 33°C. The sleeping climate created by Alpine wool under a blanket or in a sleeping bag comes very close to this ideal temperature. Other substances can only manage this to a lesser extent. Synthetic duvets in particular are clearly inferior to wool, especially to Alpine wool. If the climate regulation does not work properly, you quickly start to sweat and kick the covers off while you sleep. Without a blanket, you cool down too much, freeze and your sleep becomes restless.
This was tested in sleep laboratories at a pleasant ambient temperature of 22°C. By the way, an alpine wool blanket is also pleasant for partners sharing a blanket: Each body’s temperature is controlled separately.
Alpine wool is a sustainable resource
Robust, natural, biodegradable and renewable: The sheep wool, in this case the special alpine wool, can be shorn annually. Wool is a product which represents responsible consumption for today’s consumers who are increasingly sensitive to the environmental qualities of clothing. Alpine wool is a natural resource that keeps on growing and degrades without residues.
Advantages of wool filling:
- Alpine wool adds balance to the climate
- Alpine wool insulates
- Alpine wool is a sustainable resource
- Alpine wool is odourless and antibacterial
- Alpine wool in the sleep laboratory
- Alpine wool is easy to care for and robust
- Alpine wool in the sleeping bag
- Alpine wool and moisture transport
Once you’ve slept in Alpine wool, you won’t want anything else. That’s a promise!
DownWool – a special combination
DownWool* is an innovative HIGH-END filling made of 70% down and 30% specially treated wool.
Down has a very high insulating capacity despite being low-weight. This makes down an excellent filling material for sleeping bags and jackets. However, down only insulates when dry. As humidity increases, its fine structure collapses and its insulating effect suffers considerably.
Wool on the other hand has very good insulating properties and absorbs moisture without losing its insulating properties. This is wool’s big advantage over down. Furthermore, wool balances the temperature and has an extra antibacterial effect. Its disadvantage compared to down, however, is that it is somewhat heavier.
We have mixed both materials in perfect harmony in DownWool
We have developed an elaborate technical process to make the down and wool fuse permanently. The big advantage of DownWool is that it is not as sensitive to moisture as pure down and therefore insulates better where there is higher humidity. DownWool has the advantage of being significantly lighter than pure wool filling.
We achieve the best insulation and a perfectly dry climate with DownWool's unique material mix, while keeping its own weight low.
DownWool can do it all:
- DownWool is less sensitive to moisture
- DownWool naturally balances out the sleeping climate
- DownWool is lightweight and provides excellent insulation
The cut, shape and construction of sleeping bags
There are basically two different cuts for sleeping bags: blanket-style and mummy-style. Both models have their respective advantages and disadvantages.
Mummy-style sleeping bags
The mummy-style is the best compromise between sleeping bag space, its packing size and weight. It models the shape of a person in lying position and minimises the air space which needs to be heated inside the sleeping bag. Because the tighter the sleeping bag surrounds the body, the better it retains its warmth. But only as long as the filling is not crushed!
Blanket-style sleeping bags
The blanket style is ideal for those who need more room to move and tend to sleep outside at temperatures above 0°C. This is a rectangular sleeping bag with or without hood that can be unzipped and unfolded completely to form a blanket.
Egg-shaped sleeping bags
For people who place more emphasis on sleeping comfort than on weight and warmth, or who find mummy sleeping bags too tight, hybrid forms such as egg-shaped sleeping bags are also available. This is a combination of the mummy and blanket styles. This has a narrow head, shoulder and foot area as with the mummy, but a very wide waist that allows freedom of movement for arms and legs.
Other shape variants
Shorter people should buy short sleeping bags so that there is not too much air in the foot area. Alternatively, you can tie the foot part beyond your feet (for children, for example), or fill up the foot area with jumpers or other clothing.
There are also sleeping bags that grow along with you, especially for children. With this type of shape, an all-round zip in the foot area can provide possibilities for extension. This makes the Grüezi bag suitable as a children’s sleeping bag for body lengths from 100 cm to 155 cm.
The length of the zip and the use of filled draught collars or lined zip cover strips contribute significantly to the insulation capacity of your sleeping bag.
Special features of the Grüezi bag models
Grüezi bag uses high-quality, uncoated and rustle-free polyester or nylon fabrics with a high fibre density (thread count), usually in rip-stop design. The high fibre density is important so that the filling does not penetrate the fabric. With rip-stop fabric, thicker and more stable threads are incorporated at regular intervals. If the fabric tears, it stops at one of these thicker threads and the damage cannot spread.
Water-repellent impregnation Bionic Finish Eco from Germany
In addition, the outer fabrics are water-repellent.
Breathability and the sleeping climate resulting in sleeping comfort are very important to us. Condensation water collects on the inside of bags made from cheap, coated materials and drips back into the filling. That is why we use highly breathable PFC-free impregnation agents.
Here we use highly breathable, skin-friendly, partly soft-brushed, light materials.
Important features of a Grüezi bag sleeping bag are: