e-shop www.spacaky-stany-batohy.cz

Spacáky a spací pytle | PRIMA OUTDOOR, s.r.o.

Home » Advice, tips » How to choose a sleeping bag

How to choose a sleeping bag

Are you wondering how to choose a sleeping bag? Our team of specialists prepared a detailed article which answers all your questions. Let us help you to better you knowledge in this area and choose a sleeping bag from a genuine Czech producer.

Before you start to browse through our unmatched widest range of sleeping bags from the biggest producer in the Czech Republic, we will try to explain to you how to choose a sleeping bag. However it is not possible (and it is not the purpose of our website) to copy technical literature or textbooks and make crash course of maths, physics, thermomechanics and other sciences for you and explain everything in detail, we tried to simplify this topic.

If you are interested in more details, we are glad to answer your question by e-mail, phone call or a personal visit at our headquarters (where you can also find our shop with complete assortment of PRIMA sleeping bags). Our employees can offer all information and answer all your questions that would help you to make the right decision. If you are not satisfied with their answers, your questions would be sent to our cooperative research workers (e.g. researchers in Technická univerzita in Liberec, Textile faculty, Textilní zkušební ústav in Brno, etc.; or Swiss federal laboratories EMPA, development department of DuPont, etc.).

Team of PRIMA OUTDOOR, s.r.o.

History and theory

Witnesses remember that in Czechoslovakia before 1989, the decision was very easy. There were (if at all) only very heavy and huge so called "dekáče" (quilt sleeping bags) and sometimes also so-called "mumie" of the same qualities. If you succeeded in getting down (it did not exist in trade network), "Unika" (it was in only one shop in the Czechoslovakia and there was a waiting list of nine months; then it could be sent only cash on delivery and in two colors – watery blue and watery red) and "Monofil" (for a wonder, it was readily available), you could sew yourself so called "péřák" (down sleeping bag) at home – without a zipper, needless to say. In so called "dekáč" you were too cold nearly all the time and in "péřák" you were too warm nearly all the time.

Development of the insulation materials and the outer fabrics took rapid leap in last years. Nowadays there are so many types that it is not possible for an amateur to really know them all. And then, everyone presents his products as only top class, the best and unbeatable. How to know which insulating and outer materials are the best? There is not one ideal material. All of them have advantages and disadvantages.

Which sleeping bag is the right one?

Despite of scientific progress it is not (and probably will not be) possible to produce an ideal universal sleeping bag. It would be perfectly permeable in hot days, air-proof when the wind is blowing, waterproof in rain and remarkably warm in bitter cold days. Of course it would be cheap, light and very small after rolling up. It is not possible to produce this type of sleeping bag – and it will never be. You simply need a different sleeping bag for the summer and for the winter. Windproof/waterproof quality and permeability are opposing qualities, meaning the higher windproof and waterproof quality, the lower permeability. And vice versa. The more permeable the fabric is, the less is it able to shelter from wind and water.

The most important principle when choosing a sleeping bag

  • We need to choose a sleeping bag that is warm enough according to the conditions in which we want to use it!
  • Based on financial potential we can choose a sleeping bag with the lowest volume after rolling up and lowest weight

It is for sure that everyone who will not respect listed sequence when choosing a sleeping bag will be displeased.

The most important quality that we are interested in above all are temperatures which the sleeping bag is appropriate for.

Thermal insulating qualities of a sleeping bag are defined by the thermal insulating ability of the insulation filling. It is in direct proportion to its specific thermal resistance and its volume. The amount of air molecules the thermal insulation filling is able to bind is the measure of its thermal insulating ability. Other qualities are only secondary and can more or less increase or decrease the specific thermal resistance - so called loft (fluffiness – ability to occupy as much volume as possible, simply how much is the sleeping bag able to blow up after being unpacked), way of sewing (sandwich, shingle), orientation of fibers in the fabric etc. The real insulating medium is not the filling itself, but the air it binds. Down or synthetic material only makes the space for the air to take up. That is why you will be cold in a huge and heavy sleeping bag made of a cheap, unbranded insulating material, but you will be warmer in a thinner and lighter sleeping bag with quality filling (preferably branded hollow fibers) and you will be the warmest in the smallest and lightest sleeping bag made of modern top class hollow fibers or microfibers.

Basically, we can divide sleeping bags into four groups: ultra-summer, summer, three-seasonal and winter. If you often spend nights in open-air during the whole year, it is ideal to have all four types of sleeping bags. If you do not want so many sleepig bags, you need to make a compromise. For example, you can leave out an ultra-summer one and sweat sometimes in summer. Now you only have three. According to the principle "better warm than cold" you can leave out a summer sleeping bag and sleep in a three-seasonal from spring to autumn. Then you only need two types. And if you do not plan to sleep in freezing temperatures (where the winter sleeping bag is simply the best), a quality three-seasonal sleeping bag is completely sufficient.

Down or synthetic materials?

Some years ago, the only synonym for a warm sleeping bag was a down sleeping bag. Recently, synthetic materials logically win over down in most custmers. Down became an exceptional material for top class sleeping bags for dry freeze in high-mountain areas where it does not rain and the humidity is relatively low. Caution! That does not apply for common high-mountain conditions, much less for Arctic and Antarctic conditions. Due to high humidity, a down sleeping bag (even with the best surface material) becomes a kind of ticket to hell in these conditions. Feather absorbs humidity very easily – not only the rain water etc, but also the air humidity. As we already know, humidity noticeably decreases the thermal insulating qualities. Who did not see damp or even soaking down sleeping bag, would not believe that the down practically disappears and you are left with just a wet cloth instead of the sleeping bag. While freezing, the wet down may even turn in pieces of ice this way. In dry conditions it take up to two weeks to dry – if it does not catch mould sooner.

Synthetic fillings

The advantage of a synthetic material is in the easy maintenance and minimum humidity absorption. A sleeping bag with synthetic insulation filling is therefore ideal for an universal use from spring to autumn. It also works well in winter, except the high-mountain dry conditions. It is the best choice whenever we do not want to spend time with regular treatment and maintenance. The biggest advantage is that we is able to dry it quickly and easily, it keeps most of its properties even when damp. You can wash this type of sleeping bag in a washing machine with a gentle program without degrading the insulating qualities (unlike down). Synthetic fibers are also the only good solution for people with allergies.

Be careful about low-quality insulation

The term "hollow fibers" became incorrectly established as a name for all synthetic fillings, but differences are wast. You can find many "no name" synthetic fillings, perchance with fictional and not registered brands (as Adi-das for CZK 30,- on markets from "mysterious" producers from the East). Its fibers are very fragile and that is why the material tears easily and decays, fibers are not hollow or it contains little percentage of hollow fibers, fibers are made of inferior or recycled materials or linked with binding materials unfit for use. Its producers do not guarantee anything. In better instance, you will be cold in temperatures that do not approach the temperatures declared by producer. In worst case there is a risk of dermal, respiration or other health issues, also for example total devastation of insulation material after first washing or after short period of use. As a common feature there is an incredibly low price of the sleeping bag that does not allow even buying the standard fabric. Caution! Even many Czech and foreign renowned companies have these types in their offer – however for higher prices (that make you think that they offer quality product).

Prefer branded materials

Branded materials have a guaranteed quality and its producers have to respect many strict technical and health standards. You should consider if you can afford buying cheap pdoducts like these.

Quality hollow fibers are several dozens cm long and the section view shows one or more hollows (of approximately circular shape). Producers can also use spiral or shaped fibers to put more air into the insulation material.

Fibers are thermally processed into an insulation fleece. Air molecules are not only between the fibers as in case of classic fabrics, but also inside of the fibers – that is why this fleece insulates better with the same weight.

Until recently, the only trustworthy branded fibers were those produced by the supranational company DuPont. We arranged them from the oldest and cheapest to the newest and best: Hollofil 608, Hollofil II, Quallofil, Thermolite, Thermolite Active, Thermolite Plus, Thermolite Extra and Thermolite Extreme.

We cannot mix up hollow fibers with microfibers. Its diameter is approximately ten times smaller than in case of the hollow fibers. There is a theory of their function: air molecules captured by a microscopic structure of the fabric should stick to its surface so the fibers do not lie on each other but on the air molecules. And the result? Fleece should contain (with the same weight and volume) more air and insulate better than the best hollow fibers. The biggest advantage of sleeping bags with this kind of insulating material should be a low weight and a small volume. However, the disadvantage here is a small resistance of very fine microfibers against mechanical forces. In comparison with the hollow fibers, they quickly lose their fluffiness and as a result they lose its insulating qualities.

The most known branded microfiber with trade name Thinsulate is produced by the supranational concern 3M. Another, comparable one, is Thermolite Micro by the competitive concern DuPont. Newly, there are the new PrimaLoft type microfibers on the market. There is a vast difference between them - for example PrimaLoft One has by approximately 20% better performance than PrimaLoft Sport and is by 60% warmer the PrimaLoft Infinity. With the new convex technology, their insulation has even by 15% higher loft and thermal insulating quality.

Although the hollow fibers and microfibers have said several advantages and disadvantages, all these materials were surpassed by Polarguard and just recently by the newest -  Climashield. They are nowadays the best material for sleeping bag insulation on the market. Both of them are made in original quality in an only one producer in the USA. That said, there are also several Asian copies of worse quality and lifespan. 

The company developed Polarguard classic a first, then a better Polarguard HV, Polarguard 3D and latest th best of them - Climashield XP/APEX. This "marvelous" material is made as only one infinite thermally binded crossed looped hollow fiber with a triangular cavity with a diameter close to microfibers. It unites all the advantages of hollow, spiral and microfibers, keeping you warm even in the extreme conditions, making them absolutely unique without a competition. In all the independent tests Climashields comes up as the best thermal insulation with the longest lifespan. Last but not least, is comes with a good compressability and softness. After switching to Climashield XP/APEX, many of our customers responded very well, leaving us satisfied to provide the best insulation in the world in our sleeping bags.


Down is a well-proven natural material with a great compressibility and shape stability. Most frequently used is the goose down. But... there is not down like down.

Eider-down is just a dreamed-of insulating material. It is not used in practice, with one exception. In the OUTDOOR fair (in Friedrichshafen, Germany) one Russian company offered a wind-cheater made of eider-down. The amount of down was pretty small. And the price? More than EUR 3,000, approximately CZK 100,000. My question how much would a sleeping bag (where you need much more of it) made of this material cost got a sincere laugh and no answer.

Instead of goose down, there is ofter used duck down. It offers lower isolating capacity and when damp there is smell a typical odor. Duck down is sometimes added to goose down to lower the price.

The thermal insulating quality of down depends on the ratio of more and less fine down. This is  seen in the numbers - 90/10, 80/20 etc, meaning  there is for example 90 % of the very fine down and 10 % of the less fine. Another quality characteristic is the fullness. It expresses total elasticity and expansibility – ability of feathers to occupy certain capacity. This quantity is measured in laboratories by internationally acknowledged method and it is denoted in cubic inches (cuin). Pure fine down (100/0) has about 950 to 1,000 cuin, mixture 90/10 approximately 650 cuin and 70/30 has 500 cuin.

Pay attention though. It is not practical to use pure fine down. Less fine down increases mechanical resistance, so the higher share of fine down (100 %), the higher is its fullness and fluffiness and the down is warmer, but in the same time, it looses its fullness and fluffiness faster and it warms less then. If the quantity of high quality down in the sleeping bag is too low, it could happen within several uses. Then the down is not able to fill the capacity of the chambers, gaps appear and the insulation ability falls by a lot. When buying, you should consider carefully if you want to conquer the Everest and you need an extremely warm and light sleeping bag which will get destroyed quiet fast or a little less warm sleeping bag you can use for several years without degradation of its qualities.

Finally, it is not possible to say that down is an obsolete material. Even the high quality and most expensive insulations do not come anywhere close to the weight and thermal insulation qualities of the goose or duck down. Who is going to bivouac in very dry freezing temperatures and needs to count each gram, he should choose a quality down sleeping bag.

Outer and inner fabric

The main requirement concerning the inner fabric is the permeability. At the same time, the outer fabric should prevent an infiltration of humidity into the insulation filling, at least to some degree. The sleeping bag as a whole should have a sufficient permeability that allows the humidity to go through to the outer surface and spread out into the air. An average human sweats out approximately 0.5 to 1.5 litres of water in a form of water steam that has to get out. In the opposite case, it devaporates into water inside the sleeping bag leaving you damp or sweaty in the morning. If you feel sweaty in a relatively thin sleeping bag, it does not have to be very warm, but the outer cloth does not let out water steam. Damp insulation filling does not insulate as good as in dry conditions and the thermally insulating qualities of the sleeping bag get worse. Damp sweaty skin, dress and inner cloth also conduct warmth away much better – which we want to prevent.

The fabric should be as light as possible to allow the best expansion of the insulating filling. The inner fabric should also be pleasant to touch. Down filling requires maximum demands on the used fabric. the fabric has to be dense enough so the down does not travel away from the chambers, but permeable enough so the water steam can go out. This is an impossible task so you sometimes sweat in your sleeping bag (do not mix up sweating with thermal comfort!) and other times down travels through the fabric. Membraned materials (e.g. Gore-tex, Gore Dry Loft, Excel Dry etc.) are used for down sleeping bags. However, its price is "astronomical" and the lifespan let's say debatable. Did you know that Swiss army stopped to use clothes made of Gore-tex and started to use fabrics based on Tactel? It was surely not a matter of money.

The microfiber fabrics made of Meryl or Tactel are widespread, used for both down and synthetic sleeping bags. They balance the quality and price for the use in rougher conditions. Classic 100% polyamid (so called nylon with water-repellent finishing) is the most usual material. Ripstop is a strengthened variation of whatever fabric, more resistant against scratch and tearing. The cheapest sleeping bags are lined with. It is indeed pleasant to touch, but quite heavy, large and easy to soil. It absorbs humidity and odors and dries for a long time. If you insist on the use of cotton, these sleeping bags are appropriate only for summer nearly maintenance-free use.


The simplest sleeping bags with synthetic filling have one quilted layer of insulation. That is not a the best idea in the three-seasonal sleeping bag.

The best solution is a "sandwich construction" with two or more independent layers.

Sometimes a "shingle construction" is used – mutually crossing belts are sewn to outer and inner cloth so sleeping bag make an impression of having more insulation. It is called a "false fluffiness", bacause the specific thermal resistance of a sleeping bag is in direct proportion to the amount of insulating material. This type of construction is much more predisposed to a mechanical damage of the insulating fleece.


For many years, individual countries had their own standards. In 2002, the European Union created a European standard for sleeping bags (for measuring and calculation of usage  temperatures). You can find its summary in a separate link.

Reliable producers or importers indicate these values. The slower ones state at least three values: maximum, comfort and extreme. If you do not find three values on a sleeping bag, but just one or two, it does not mean that the sleeping bag is bad. The author just tries to confuse the client. The client than could think that an extreme temperature means the same as a comfort temperature... and the extreme temperature is absolutely not an allowable temperature you should risk spending the night in such sleeping bag in.

Do not celebrate prematurely though...

All given values are valid only in ideal laboratory conditions and for a standard man or woman!

In reality, the usage conditions of the sleping bag are extremely changeable. It is a countless combination of following factors:

  • temperature of the surrounding air
  • radiation temperature of the surrounding air
  • speed and whirling of air
  • humidity captured in the sleeping bag and the surrounding humidity
  • user's clothing
  • user's position in the sleeping bag
  • insulation between sleeping bag and ground and thermal insulation of the ground
  • compression of the sleeping bag by the weight and volume of its user
  • other than ideal surface and volume of the user and space of the sleeping bag ratio

Physiological reactions that are determined by the surrounding conditions and determine discomfort and risk of hypothermia are very variable according to the body temperature, cold hardiness, sex etc. Each of us has a different blood circulation, different metabolism and we sweat different amount of water during the night. These factors noticeably influence the subjective feelings of cold or warmth. In case of each individual, there can even appear changes during the time, e.g. due to fatigue, food, body situation, etc. They are influenced mainly by the climatic conditions, quality of the insulating underlay, physical shape, etc.

The basal metabolism is very individual. Practical measurements shown the specific values measured in individuals in laboratory condictions vary conciderably. About 5% of the population has the metabolism faster by up to 30%. In one study, there were 150 persons measured and the basal metabolism ranged from 1027 kcal/den to 2499 kcal/den. In reality, if the producer lends the same sleeping bag to 2 individuals of the same highth, weight and body volume, one can produce as much energy as the second would while running fast, for example. Is the sleeping bag cold or unbearably hot? Which one is right? 

Finally – the perception of cold is alway subjective!

Temperature conditions of using are not only quantities resulting from the inner essence of a sleeping bag but it depends on the using conditions, individual person and their shape in the time of use.

Is the norm wrong then? Oh no, do not lose hope. It is not necessary to be a specialist to know that a sleeping bag that weights 1 kg and is intended for 30 °C below zero is suspicious. Even a total amateur can more or less compare sleeping bags from different producers after reading this article. The most important is the type and weight of the insulating material. When deciding between two types we recommend to choose the warmer one – especially when you are a woman. One never knows when they will need a temperature reserve and when the sleeping bag has a side zipper, it is not necessary to be afraid of redundant warmth. Some extra grams (however they become heavy during the day) will get back to you in form of a comfortable deep sleep through the night. Expenditure of energy during the night in a sleeping bag when you feel cold is always higher than expenditure of energy when you carry extra half a kilogram. No kidding.

Simple instructions based on this chapter:

Every time choose a sleeping bag with a sufficient warmth insulating reserve. Data on the tag do not mean that you will feel comfortable in any conditions - you would only feel comfortable in ideal laboratory conditions that you will not meet in reality. And how big reserve should you choose? It depends only on you and the conditions you can experience.

That means the temperature range of a sleeping bag is just an orientation value that results from a thermal insulation measurement of the sleeping bag and analysis of this measurement regarding temperature usage that helps to compare types of insulating materials and sleeping bags – in standardized conditions.


The right size is very important. A small body will not heat an excessively large sleeping bag and vice versa – too small sleeping bag (that will not allow comfortable stretching of the body) compresses the insulating layer which then works less.

A sleeping bag should be moderately loose so the sleeper does not turn with the sleeping bag but only turns himself when moving. Producers of sleeping bags usually have two sizes regarding height of the figure.


Nowadays, sleeping bags without a zipper are practically not produced. However, a zipper and a zipper is not the same thing. In case of unbranded zippers you risk that it will betray you in the moment when you need it the most. Cold night spent in a sleeping bag used as a blanket because you can not fasten it, it breaks down or a slider came off can be your last night. Zippers from YKK are the absolute world top class, Czech zoippers Ws20 are also very good.

Zipper should be covered with an inner belt that prevents the escaping of heat through the zipper. All types of PRIMA sleeping bags have their zipper covered with belt.

Warm seams

We should not find so-called cold seams, sewing through all the layers of a sleeping bag, not even in the case of simple-constructed sleeping bags. If you elevate opened sleeping bag against the light and you can see gaps where the needle came through and through, get rid of this type of sleeping bag.

You cannot find "cold seams" in case if PRIMA sleeping bags.

Compression case

Yes, a compression case enables to compress the volume of the sleeping bag up to 40 % of its original volume but each of this compressions lowers the lifespan of the insulation material, both synthetic and down. Fluffiness imperceptibly descends and the sleeping bag blows up less after unrolling.The longer and more often the sleeping bag is compressed, the worse.