The sleeping bag is part of the basic tackle of the trekker. If a simple bag or even a bag of meat is enough for nights in a shelter or a lodging of the stage, the choice of a good bag is necessary if you sleep under the tent, a fortiori if you go on a trek in altitude.
The head is, like the feet, the first zone of heat loss (nearly 30%). You will need a perfectly fitted hood. Check the effectiveness of the clamping system (cords or other). Finally, the hood works in conjunction with the shoulder collar for perfect insulation of the upper part of the body.
Equipped with a Velcro closure and a drawstring, the collar makes it possible to obstruct the only zone of communication with the outside cold. Ideally, it can be manipulated with one hand. Always to fight the cold, the zone of the feet generally benefits from a more consistent insulation.
THE TEMPERATURE INDEX
Depending on their calorific capacity, the sleeping bags are divided into four programs: one, two, three or four seasons.
– The “one season”, very light and mainly synthetic, have very limited use. The “two seasons”, a little more efficient, will do the job throughout the spring, but in the temperate zone.
– The “three seasons” will cover most of the trekking needs, with a relatively wide range of use, from March to November. Their comfort temperature is located around 0 ° C., within plus or minus 5 ° C. However, they will find their limits in the middle of winter when the temperatures happily pass the zero bar.
– The “four seasons” thus come to complete the picture with temperatures of the comfort of +/- 10 ° C. Trimmed for the harshest conditions, some of them even offer total well-being by -30 ° C.
– The natural lining (feather and down) offers exceptional insulating qualities thanks to its swelling power. It is also very light, very compact and especially ultra comfortable. But once wet, the feathers lose all their insulating power.
– Sleeping bags with synthetic lining are certainly less comfortable, less efficient, less compactable, heavier, but they do not fear moisture, the hollow fibers the component being hydrophobic.
The sarcophagous sleeping bags are much more suitable than the so-called “open” bags for effective thermal insulation since they guarantee a maximum hermeticity and make it possible to shelter the head, this being the first zone of leakage of the body heat. Their profiled cut and close to the body greatly limits the circulation of the air.
Slides are often the Achilles heel in terms of air tightness. A quality bag must be equipped with flaps above and below the closing zips. With flaps, no worries. Some bags are twin (left or right). To be monitored when buying.
In order to obtain a good sleeping bag, it is not enough simply to fill an envelope of upholstery fabric, because it would quickly become packed in certain areas, thus creating thermal bridges through which heat loss occurs. Thus, the more numerous the compartments (or boxes), the better the packing stays in place and the more efficient the latter.
A prime criterion in choice!
– In length, your shoulders should be totally enclosed by the shoulder collar, so you must keep a certain margin at both ends (do not hesitate to exaggerate your size, it is always bigger in the lying position, never sleeps the feet square).
– For the width, find the right middle. Too narrow, you will not be able to move inside; too wide, the time to warm up will be longer and the risk of heat loss higher.