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How to choose a sleepeing bag

You do not know how to choose your sleeping bag? Our team of specialists prepared detailed article which answers all your questions. Let us help you to better you knowledge of this problematic and choose a sleeping bag from a genuine Czech producer!

You do not know how to choose your sleeping bag? Our team of specialists prepared detailed article which answers all your questions. Let us help you to better you knowledge of this problematic 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 sleeping bag. However it is not possible (and it is not purpose of out web side) 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 receive your question by e-mail, phone call or personal visit at our headquarters (where can you also find our "shop" with complete assortment of PRIMA sleeping bags). Our employees can supply all information to you 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 or 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.

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History and theory

Witnesses remember that 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 feathers (it did not exist in trade network), "unika" (it was only in only one shop in the Czechoslovakia and there was waiting list – it took nine months to get it; and it could be sent only cash on delivery and only in two colors: watery blue and watery red) and "monofil" (for a wonder, it was readily available) you could sew so called "péřák" (feather sleeping bag) at home – needless to say without zip. In so called "dekáč" you felt nearly all the time cold and in "péřák" you felt nearly all the time warm.

Development of insulating materials and superficial clothes noted immense leap in last years. Nowadays there are so many types that it is not possible for amateur to know them a lot. And then, everyone presents that just his products are top class, the best and unbeatable. How to be well informed regarding insulating materials and superficial materials? There is not one ideal material. All materials have advantages and disadvantages.

Which sleeping bag is the right one?

Despite of scientific progress it is (and probably will not be) not possible to produce ideal universal sleeping bag. It would be perfectly permeable in hot days, air-proof when the wind is blowing, waterproof in rain and fantastically 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 not ever be. You simply need different sleeping bag for the summer than for the winter. Windproof/waterproof quality and permeability are opposing qualities, it means the higher windproof quality (perchance waterproof ) the lower permeability. And vice versa. The more permeable cloth is, the lower is able to prevent from wind and water.

The most important principle when choosing a sleeping bag

  • We have to choose sleeping bag that is warm enough according to conditions in which we will use it!
  • Based on financial potential we can choose sleeping bag with the lowest volume possible after rolling up and the lightest one.

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

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

Thermal insulating qualities of sleeping bag are defined by thermal insulating ability of insulating filling. It is in direct proportion to its specific thermal resistance and its amount. Thermal insulating filling criterion is the amount of air molecules that it is able to attach. Others are only secondary qualities that can more or less decrease specific thermal resistance. So called "loft" (fluffiness – ability to occupy as huge volume as possible, non-professionally, how much is sleeping bag able to blow up after being unpacked; way of sewing (sandwich, shingle), orientation of fibers in cloth etc – these are the important factors. The real insulating medium is not the used filling, but air. Feather or synthetic material just makes space for the air to occupy. That is why you will feel cold in huge and heavy sleeping bag made of cheap, unbranded insulating material, but in thinner and lighter sleeping bag with quality filling (preferably branded hollow fibers) you will feel more warm and in the smallest and lightest sleeping bag made of modern top class hollow fibers or microfibers you will feel the warmest.

Simply said, we can divide sleeping bags into four groups: ultra-summer, summer, three-seasonal and winter. If you often spend nights in open-air and during the whole year, it is ideal to have four types of sleeping bags. If you do not want to have so many sleeping bags, you will have to make a compromise. For example this way: leave out the ultra-summer one and in summer you will sometimes sweat. Now you have three of them. In accordance with principle "better warm than cold" you omit summer sleeping bag and from spring to autumn you will sleep in three-seasonal. Then you need just two types. And if you do not plan to sleep in freezing temperatures (where the winter sleeping bag fits the best), good three-seasonal sleeping bag is sufficient.

Feather or synthetic materials?

Few years ago, the synonym for the warm sleeping bag was a sleeping bag made of feathers. In recent years, synthetic materials win logically over feathers that became exceptional material for top class sleeping bag for "dry" freeze in high-mountain areas where it does not rain and the humidity is relatively low. Attention! Not for common high-mountain conditions, much less for arctic and Antarctic conditions! Because of high humidity, a feather sleeping bag (however with the best outer cloths) becomes something like ticket to hell in these areas! Feather absorbs humidity very easily – not only the water itself when you are sleeping in the puddle or in the rain, but also the air humidity. As we already know, humidity noticeably decreases thermal insulating qualities. Who did not see dumpish or even soaking feather sleeping bag, would not believe that feather practically disappears and instead of sleeping bag you have just wet cloth. In high freeze, you just transfuse hailstones that were feather before. Then you have to dry soaking feather sleeping bag in dry conditions for one or two weeks – of it does not sooner become mouldy.

Synthetic fillings

The advantage of synthetic material is in unassuming maintenance and in minimum humidity absorption. Sleeping bag with synthetic insulating filling is ideal for universal use from spring to autumn – always. And it also works as a winter type except high-mountain dry conditions. Also whenever we do not want to burden ourselves with regular treatment and maintenance. The advantage is that it is possible to dry it easily and quickly and even wetting does not overly degrade its qualities. You can wash this type of sleeping bag in washing machine at a soft program without devaluation of insulating qualities - as in case of feather sleeping bag. Synthetic fibers are also the only solution for people with allergy to feather.

Be careful about low-quality insulation

The term "hollow fibers" became incorrectly established as a name for all synthetic fillings, but differences are usually abysmal. 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 cloth 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 feel cold in temperatures that do not approach to temperatures declared by producer, in worst case there is a risk of dermal, respiration or other troubles, or for example total devastation of insulating cloth after first washing or after short period of use. As a common feature there often appears incredibly low price of the sleeping bag that does not allow even buying the standard cloth for sewing. Attention! Even many Czech and foreign renowned companies have these types in their offer – however for higher prices (that makes you think that they offer quality product).

Prefer branded materials

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

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

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

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

We can not mix up hollow fibers with microfibers. Its diameter is approximately ten times smaller than in case of hollow fibers. There is a theory of their function: air molecules captured by microscopic structure of cloth should stick to its surface so the fibers do not lie on each other but on the air molecules. And the result is? Fleece should contain (with same weight and volume) more air and insulate better than the best hollow fibers. The best advantage of sleeping bags with this kind of insulating material should be the low weight and a small volume. However, the disadvantage here is a small resistance of very fine microfibers against mechanical expose. In comparison with hollow fibers, they quickly lose fluffiness and as a result they lose its insulating qualities. The well-known branded microfiber has trade name Thinsulate and is produced by supranational concern 3M. Another, comparable one is Thermolite Micro by competitive concern DuPont.

Hollow fibers and microfibers have several advantages and disadvantages. Recently DuPont concern developed three-part insulating fleece. It contains microfibers, hollow fibers and spiral fibers. The trade name for this insulation is Thermolite Extreme and nowadays, it is the best insulation material in the world.

Recently, all of these insulation materials were surpassed by Polarguard materials. Gradually Polarguard was developed, after that improved Polarguard HV originated and finally - the best you can buy today in the world - Polarguard 3D. This "magical" material is made of one infinite thermally linked crossed looped hollow fiber with triangle hollow and its diameter approaches to microfibers. It combines all advantages of hollow and spiral fibers and microfibers, keeps heat in the most challenging conditions and nowadays it has no competition. Usually, it is something for something: hollow fibers have good lifetime and worse insulation quality, microfibers vice versa. Polarguard 3D according to independent tests: it has the best insulation qualities and the best lifetime. Miracles happen. Its outstanding qualities are: good compressibility and softness. There is also Polarguard Delta. According to the opinion of producer, it has of about 3 % higher insulating qualities than Polarguard 3D. Outer diameter of fiber is the same as in case of Polarguard 3D, but the triangle hollow is bigger. It should contain more air this way – but the wall of fiber became thicker. Its lifetime decreased in so far that when we measured insulating fleece or the sleeping bag, every time we got worse results than in case of Polarguard 3D. Also multiple responses from users persuaded us that Polarguard 3D is the best insulating material for sleeping bags in the world.


are well-proven natural material with good compressibility and very good shape stability. Goose feathers are the most frequently used ones. But... there are not feathers like feathers.

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

Instead of goose feathers, duck feathers are often used. But it performs lower fullness and after getting wet you can smell typical odor. Sometimes, goose feathers are extended with duck feathers.

Thermal insulating quality of feathers is dependent on the ratio of down and small feathers. These are the numbers: 90/10, 80/20 etc. The first means that there is 90 % of down feathers and 10 % of small feathers. Another quality feature is so called "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). Plain downy feather (100/0) has about 950 to 1,000 cuin, mixture 90/10 approximately 650 cuin and 70/30 has 500 cuin.

But pay attention. It is not practical to use plain down feathers. Small feathers increase mechanical resistance: so, the higher share of downy feather (100 %), the higher is its fullness and fluffiness and the feather is warmer, but in the same time, it losses its fullness and fluffiness more quickly and it warms less. And if the weight of very quality feathers in the sleeping bag is too low, it could happen within several usings. After that the feathers are not able to fill the capacity of chambers, gaps come up and a draft starts to blow through – and then you have not much of a summer sleeping bag. When buying, you must consider carefully if you want to conquer Everest and you need extremely warm and light sleeping bag (which will get destroyed quickly) or a sleeping bag that is not so warm but that you can use for several years without degradation of its qualities.

Finally: it is not possible to say that feather is obsolete material. Even the high-quality and most expensive fillings do not come anyway close to the weight and thermal insulation qualities of the goose or down feathers. Who is going to bivouac in high dry freezing temperatures and must count each gram, he should choose quality feather sleeping bag.

Outer and inner cloth

Main requirement concerning inner cloth is permeability. At the same time, the outer cloth should prevent infiltration of humidity into insulating filling, at least to some measure. Sleeping bag as a whole should have sufficient permeability that allows humidity to go through to outer surface and spread out into the air. Average human sweats out about 0.5 to 1.5 litres of moisture in form of water steams that have to get out. In the opposite case, it devaporates in the sleeping bag into water and in the morning you will be wet or sweat. If you sweat in relatively thin sleeping bag as well, it does not have to be very warm, but the outer cloth does not let out water steam. Damp insulating filling does not insulate as good as in dry conditions and thermally insulating qualities of sleeping bag get worse. Also damp sweat skin, dress and inner cloth conduct warm away much better – and we want to prevent it.

Cloth should be as light as possible to allow the best expansivity of insulating filling. Inner cloth should be also pleasant to touch. Feather filling constitutes maximum demands on used cloth. Cloth must be dense enough so the down feathers and small feathers could not penetrate from chambers, but permeable enough so the water steams could go out. This is infeasible task so you sometimes sweat in your sleeping bag (do not change sweating with thermal comfort!) and other times feathers go through the cloth. Membraned materials (e.g. Gore-tex, Gore Dry Loft, Excel Dry etc.) are used for feather sleeping bags. However, its price is "astronomical" and lifetime, 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 surely was not a matter of money.

Widespread materials are these microfiber materials made of Meryl or Tactel that are used for both feather and synthetic sleeping bags; the quality and price are in balance 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 variant of whatever cloth that is more resistant against scratch and tearing. The cheapest sleeping bags have cotton inside. It is indeed pleasant to touch, but quite heavy, large, easy to soil, it absorbs humidity and odors and it dries for a long time. If you insist on using 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. It is not a good idea for the three-seasonal sleeping bag.

"Sandwich construction" with two or more independent layers is the right solution.

"Shingle construction" is sometimes used – mutually crossing belts are sewn to outer and inner cloth and sleeping bag looks like there is more insulating filling than there really is. It is called "false fluffiness". Specific thermal resistance of sleeping bag is in direct proportion to the amount of insulating material; this type of sleeping bag is much more predisposed to mechanical damage of insulating fleece.


Czech Republic joined the European Union. Whether we like it or not, one result is that we have to adhere to European standards.

Literature features that there are no standards for using temperatures of sleeping bags. You may find it surprising that for many years, individual countries have their own standards. Since 2002 European standard for sleeping bags has existed (exactly for measuring and counting temperatures). You can find its summary in a separate link.

Reliable producers or importers do indicate these values. The slowest of them state at least three values: max., comfort and extreme. If you do not find three values on 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 extreme temperature means the same as comfort temperature... and extreme temperature is absolutely not an allowable temperature you should risk spending the night in such sleeping bag in.

Finally everything in order? Do not triumph before time...

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

In practice, the conditions when using the sleeping bag can be extremely changeable. Every time it is the combination of following factors:

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

Physiological reactions that are determined by the surrounding conditions and that determine discomfort and risk of hypothermia are very variable according to 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 influence noticeably subjective feelings of cold or warm. In case of each individual, there can even appear changes during the time, e.g. because of fatigue, food, body situation, etc. They are influenced mainly by climatic conditions, quality of insulating underlay, physical shape, etc.

And finally – the perception of cold is subjective!!!

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

So... everything is wrong? Oh no, do not lose hope. It is not necessary to be a specialist to know that sleeping bag that weights 1 kg and is intended for 30 °C below zero is suspicious. Even 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 insulating material. When deciding between two types we recommend to choose the warmer one – especially when you are a woman. One never knows when he will need temperature reserve and if the sleeping bag has side zip, it is not necessary to be afraid of redundant warm. And some extra grams (however they become heavy during the day) will get back in form of a comfort, tight sleep through the night. Expenditure of energy during the night in 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 sleeping bag with sufficient warm insulating reserve. Data on tag do not mean that you will feel comfortably in any conditions - you would feel comfortably only in ideal laboratory conditions that you will not meet in practice. And how big reserve you should choose? It depends only on you and conditions you could experience.

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


Right size is very important. Small body will not "heat" excessively large sleeping bag and vice versa – too small sleeping bag (that will not allow comfortable stretching of body) compresses insulating layer - and than it insulates less.

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


Nowadays, sleeping bags without zip are practically not produced. However, zip and zip is not the same thing. In case of unbranded zip you risk that it will betray you in the moment when you need it at least. Frosty night – spent in sleeping bag used as blanket because you can not fasten it, it breaks out or slider came off – can be your last night. Zips YKK are the absolute world top class, Czech zips Ws20 are also very good.

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

Warm seams

We should not find so-called "cold seams" (it means sewing through all the layers of 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 can not find "cold seams" in case if PRIMA sleeping bags.

Compression case

Yes, compression case enables to compress the volume of the sleeping bag up to 40 % of original volume but each of this compressions lowers lifetime of the insulating material – synthetic and feathers as well. Fluffiness imperceptibly descends and sleeping bag after unrolling blows up less. And the longer and more often the sleeping bag is compressed, the worse.