Characteristics of a Sleeping Bag

The sleeping bag is the element that will allow us to spend a night in the mountains, either in a shelter or bivouacking, causing the temperature of our body is kept in the appropriate limits to achieve a pleasant and restful sleep to continue our activity the next day with sufficient strength. Below we will detail in a technical each of the component parts of a sleeping bag. Once you have read this article, you can read the related operation and maintenance thereof.

Before proceeding, we first need to know is how a sleeping bag. The heat generated in the interior of the bag is the very heat that we generate when we are inside. The sole function of the sleeping bag is to keep the heat and prevent loss. Therefore, no bags "magic" that produce heat or sacks hotter than others.

How loses heat a sleeping bag? There are four phenomena that make a sleeping bag loses heat from its interior and thus, decrease the temperature . These are evaporation, radiation, conduction and convection. Let's see what are each of them.

Evaporation Moisture that transpires our body should go outside the bag as quickly as possible, because when we stay inside enfriaríamos reducing the temperature of the bag.
Radiation: Any body radiates heat to the outside, especially how much lower the outside temperature, hence the bag should provide some mechanism to prevent that heat can escape from the same bag.
Driving: Two bodies in contact transpasan heat until they are evenly matched. Being the ground at a temperature lower than us, we would be constantly giving heat that we generate. Therefore, a good insulation is very important to bedtime on the ground.
Convection: Hot air tends to escape and give way to cold air. Hence sac openings are another important point of heat loss inside, especially on windy nights, warm nights while in what you get is a nice freshness.
Now that we know the functioning of the bag and what are the main problems that must fight, we will proceed to detail each of the parts that are made ​​by analyzing what their functions, advantages and disadvantages.

Filler or insulation

The filler material is the most important when choosing a good sleeping bag that suits our needs, and is that going to take much of the responsibility for the final price of the same.

The filler material creates a layer of air inside, which is responsible for maintaining maximum heat inside the sleeping bag. A higher air layer, heat retention in May. Hence the areas in which the sac more crush our weight, are most prone to heat loss.

We can find three groups of bags according to the filler material, such as down, of the synthetic fiber and cotton. We explain the advantages and disadvantages of each.

a) fuzz

It is a natural product and its performance is unquestionable. It is the material that provides greater heat retention, lighter and better compression, but the disadvantage is its high price and long drying time when used in high humidity areas. You have to know that a wet sack loses its functionality.

Typically the bags are not made from 100% down, if it is not mixed with other types of feathers and filaments that make losing quality. A greater amount of down, greater effectiveness. This relationship is expressed as 90/10, which indicates 90% down and 10% feather (this would be the highest quality we can find down in a sleeping bag). Pay attention to this value always, since many come with a 50/50, which will cause the result is not the same as much as we can sell it as a down sleeping bag.

The down bags are usually announced in stores and catalogs in the same category "bags of feathers." Therefore, we must look at the specifics to see how much each one leading down.

b) Synthetic Fiber

It is an unnatural product with very similar performance to down, usually manufactured with polyester fiber . Its major advantage is price and fast drying time, ie, works best in high humidity. One drawback is its higher compression and worse.

Each manufacturer has its own synthetic fiber, with its technical name, here we do not analyze them all. There are many websites where you can compare them once you have you know which ones have the bag you are looking.

c) Cotton

For the mountain never use a sleeping bag of cotton despite its softness and good moisture absorption capacity generated by perspiration. The bags of cotton are very heavy and when it may be difficult cake decompacted. Therefore only recommended for campsites, so we will not discuss them in this article.

Weight amount of filler and

The amount of filler is that which will fix the heat retaining capacity of the bag, so that more filler, the higher the temperature that may be retained inside the bag. But keep in mind that does not harbor the same 1 kg of down to 1 kg of synthetic fiber, although many of them may be able to obtain almost similar. Therefore, this feature will always couple to fill type described above.

Many manufacturers specify the amount of filler in g/m2 instead of indicating the total number of grams of the same.

The total weight of the bag is also an aspect to take into account when we carry him in our backpacks and make a trek. Although further the weight is given by the amount of padding that holds the sack will also be added outdoor fabrics, zippers, compression bag, etc.


The baffle refers to the distribution of filler material throughout the bag. All have in common tabicados divide the sleeping bag in small areas separated from each other in which to introduce the material. This is done so that the down or pile fiber is not all on one side of bag, and so is uniformly distributed.

What one hand solves the baffle, land fill, is itself the beginning of another point of heat loss, as the seams for the different areas of the baffle will not fill material to prevent heat loss . Manufacturers use different types of tabicados to get around this problem.

Swelling or expanding capacity

The swelling capacity (fill power) refers to how the padding inside expands and thus, how big will the air layer is formed and prevent heat loss, as already discussed above.

In the down inflated capacity is measured in "cuins" (cubic inches or cubic inches), and the larger the greater the swelling capacity. We can find three main types:

Up to 500 cuins -> poor quality.
Between 500 and 600 cuins -> Medium.
Over 700 cuins -> High quality.
This measure is not used when the filling material is synthetic fiber, since it is not capable of swelling.

Exterior Material

The outer material is the material most visible of a sleeping bag and protects the filler. However, it is also very important to build and we often forget to give the attention it deserves.

A very fine fabric will obviously be lighter, so it will gain in weight, but may be less resistant and leave through the filler material, so we'll have to be more aware of their care and management.

Furthermore, a tissue usually not very resistant to moisture, but allows faster drying and a better evaporation.

We can even find sleeping bags with waterproof membrane like Gore-Tex, but this is reserved more for the sleeves bivouac.

And volume compressibility

The ability to measure how much compression will reduce the filling material. This factor, along with the other materials compressibility (as foreign tissue) will determine the final volume of the folded bag, which is extremely important when transporting it inside a backpack. As discussed above, the down has much more capacity than the synthetic fiber compression.

Normally, manufacturers report the volume by external measures sac uncompressed and compressed.

The bags usually come with a bag in which to store and transport it comfortably. If this sleeve also possesses tape to compress the bag, is called compression sleeve. Importantly, the bag must spend as little time as possible in a compression sleeve (only during transport in backpack), however, discuss the issue of maintenance and care in a separate article.

Size and shape

Why are such important measures sac? A sack too large will cause a layer of air exists inside much larger and more job costing us warm. At the same time, a sack too narrow will not allow us to move freely (hurting our rest), or we can store objects inside (as personal or water containers on very cold nights). Therefore, the best solution is a custom bag, but this is going to drive up the final price.

We can find two types of sleeping bags by shape:

Rectangular: They are very spacious and comfortable if we use them to sleep in very warm, and we can open them completely and use as a blanket. But nothing recommended in very cold nights.
Mummy: As regards insulation and other properties, this is the most effective because weighed and occupy less. Its shape adapts to the body: the knees down is narrower, in order to have less volume of air to heat and without being too tight so that the feet do not compress too much and lose heat insulating layers.

Rectangular type (Ferrino Travel)
Rectangular type (Ferrino Travel)
 Type mummy (North Face Lynx)
 Mummy (North Face Lynx)
Images property of the individual manufacturers referred sleeping bags.

Zippers should be resistant to stress, dirt, wear and cold. They should be able to open the bag in both directions (neck or feet) ventirlarlo to and from both sides (from outside or from within).

This is the weakest point in the construction of the bag, as it represents an important point of loss of heat, so that bags of a spice bring higher performance or thermal band collar along the entire rack, even with the same filler material as the rest of the bag, to avoid these losses.


The hood can vary from bag to bag summer winter. For a summer coat hoods tend to be wider and open, while for a winter coat is better to have a tighter hood which does not permit air entry, ie, heat loss by convection. On cooler evenings, it would be appreciated that the hood has its own fill and elastic bands that allow a better fit to our head.


The collar stands up to the neck in the sleeping bag, just under the hood, and its function is to prevent air from entering the bag and convective heat loss, especially in the back. Usually accompanied by some sort of cord inside to adjust once we're in the sack.

Temperature ranges by manufacturer

According to the European standard EN13537 on requirements sleeping bags, all labeling must show in their four temperatures: higher maximum temperature, the comfort temperature, temperature and extreme temperature limit. These temperatures are obtained from tests performed with puppets and simulating different weather conditions, hence serve only as a guideline. It is important to note that each person's metabolism is different, and their resistance to cold also.

The maximum temperature is higher than that to which a man can sleep without sweating too much with the hood open and arms out (sometimes omit this value labels).
The comfort temperature is that at which a woman can sleep comfortably in a relaxed position.
The temperature limit is one to which a man can sleep huddled all night without waking.
The extreme temperature is that at which a woman can hold up to six hours without danger of death from hypothermia.
For this classification is considered a man of 25 years, with a height of 1.73 m and a weight of 73kg, and a woman of 25 years, with a height of 1.60 m and a weight of 60 kg.

Once you know the features, it is now your turn to learn how to use and maintain the sleeping bag to get more out.

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