The comfort temperature and limit temperature are the parameters that you can find very often. They are on the bag of the sleeping bags, quilts, or comforters. It is a laboratory model developed to standardize the parameters provided by the manufacturers. In Europe, it is described for, sleeping bags only, in the European Standard EN 13537. It assumes a whole range of standard parameters such as no wind, dry air, no interaction with the ground, or hammock.
He is a 25-year-old healthy man, 1.73m high, weight. She is a 25-year-old healthy woman, 1.60m high, 60kg weight. According to this model, the comfort temperature is the woman’s skin surface temperature not lower than 32,8OC. The limit is the temperature of the man’s skin not lower than 32,9. The lower temperature of the skin is termed as cold.

Intuitively, we feel that the comfort temperature is when it is neither too warm nor too cold. This feeling is very subjective. Usually, the comfort temperature is described rather as a range of surrounding temperatures. It’s between 16oC and 22oC

In fact, thermal comfort is depended on quite a lot of internal and external factors that should be considered:

Internal factors –  those that lie within us:

  • Acclimatization

Nothing else than getting used to the surrounding conditions. The same temperature in the winter seems to be high, and in the summer – low.

  • Warming up

The body tolerates low temperatures better when is warmed-up (for example by physical exercises before sleep).

  • Fatigue / hunger

When you get tired or hungry, your resistance to low temperatures decreases. This also happens with the reduction of adipose tissue (e.g. with grueling lifestyle).

  • Age

Generally, as we get older, the resistance to the low temperatures slowly decreases.

  • Gender

It is assumed on the basis of studies, that the comfort temperature for men is up to 7oC lower than for women. Often, the “male” comfort temperature is defined as the comfort limit (limit).

  • Alcohol

One of the more tricky factors – gives a short-lasting feeling of warmth. It is because alcohol dilates the blood vessels and causes warm blood to flow to the skin. However, the blood cools down quickly and eventually leads to faster cooling of the body, contrary to the initial feeling of warming up. In addition, people after drinking alcohol are less responsive to temperature changes, and therefore cover themselves inadequately to the prevailing weather conditions.

External factors – the most important are:

  • Real temperature

Basic factor – true temperature, measured in a shade (usually 2m above the ground). Moreover, the temperature of a place to sleep (ground, hammock, sleeping pad, etc.), is a very important parameter. Lack of proper thermal insulation (mattress, uderquilt, etc.) can cause the fast cooling down of the body regardless of the thermal insulation level of a sleeping bag or quilt.
Hammock “cold butt syndrome” is a perfect example of the problem described above. The sleeping bag insulation is crushed by the body and the hammock that wraps around. The sleeping bag practically does not protect against hypothermia in the place where the body sticks to the hammock.

  • Humidity

The general principle is as follows: an increase in the humidity intensifies unpleasant feelings.
When it is warm, the higher humidity potentiates feeling hot. When it is cold, the higher humidity gives the impression of freezing cold. Humidity and moisture remove heat from the body surface.
A wet coat is an exceptional situation. Water cools the body 20 times faster than dry air, which underlines the importance of humidity and moisture.
Puffing or covering the mouth and nose with a duvet or sleeping bag is not recommended. The breath temporarily heats the air but, above all, increases the humidity.

  • Wind

As wind speed increases, the actually perceived temperature decreases. The heat generated by the body is carried away, therefore we feel particularly cold under windy conditions. Such a lowering of body temperature caused by the low-temperature air is referred to as the wind chill effect.

The table below shows the relationship between the actual temperature, wind speed, and wind chill.
Of course, this is a significant simplification. It does not take into account the second extremely important external factor, humidity.
It does not take into account, from obvious reasons, human internal conditions.
However, due to the simplicity of the measurements (a thermometer and the ability to recognize wind speed or anemometer is enough), it remains one of the most useful ways to assess the temperature felt in the field.

  • Additional insulation

Usually, it is simply an extra layer of not too tight (it worsens proper blood circulation) clothes. The hat deserves special attention. Contrary to the general assumption, we do not lose more heat through the head than through any other parts of the body. However, the head is almost fat-free and, due to its location, more exposed to temperature fluctuations.

For all these reasons, information about the comfort temperature that we can find on the packaging of the sleeping bags or quilts should always be treated with the utmost caution.
After buying a new sleeping bag/comforter, quilt, etc. you should simply use it for the first time under controlled conditions.
Check your body reactions (consider the medical condition and other factors described above). It would be best, of course, if the conditions were similar to those expected during the trip.
It is absolutely necessary to ensure the possibility of additional heating of the body (e.g. an additional blanket, heater, thermos, hot water bottle, etc.) to avoid any possible cooling down.
It’s a good practice to test the equipment in the presence of people who ensure safety. Waking up every few hours (e.g. two) and controlling your condition is a rather onerous but practiced solution.
This is especially important when the predicted temperature values may fall to the levels that are dangerous to health or life.

Good practice:

  • Before you go outdoor, test your sleeping bag, quilt or another cover in the controlled conditions.
  • Protect your sleeping place from wind and rain (e.g. use the Tarp).
  • Warm-up your body and eat something before sleep.
  • Satisfy physiological needs.
  • Put on dry clothes, including a cap.
  • Do not cover your mouth and nose.
  • Do not drink alcohol before sleep.