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All wrapped up03.02.2015 - (idw) Hohenstein Institute
Warm outer layers for cold days
BÖNNIGHEIM (ri) "There's no such thing as bad weather - just the wrong clothing".
Every year, sudden changes in the weather and icy temperatures make this truism
topical once again. But what functions does clothing have to fulfil and how do modern
materials accomplish that? Dr. Andreas Schmidt, Head of the "Function and Care"
department at the Hohenstein Institute in Bönnigheim, studies and improves the
wearing comfort of clothing and knows the answers to these questions:
What are the main functions of clothing?
Clothing helps people to survive in the ambient conditions. That is to say, on the one
hand, it has to keep us warm, and, on the other, it has to allow sweat to evaporate so
that the body is kept sufficiently cool when necessary.
Why do we wear clothing instead of having fur?
The loss of our fur was a milestone in the history of our becoming human. Almost
all mammals regulate their body temperature by respiration, but this greatly restricts
the scope for heat dissipation. Early man, on the other hand, used his entire body for
heat dissipation, making him superior to most other animals in terms of stamina and
adaptability. However, the ability to sweat is only really effective if there is no fur to
hinder air circulation. That is why in the course of evolution man largely lost his body
Consequently, early man was only able to settle in colder regions of the world by
inventing protective clothing. Nevertheless, even in climatic regions where protection
for the body is not actually necessary, in the course of our cultural development typical
types of clothing have still come to be worn for ethical and religious reasons.
Why does our body need to be protected from the cold?
Like all mammals, humans are warm-blooded, and their temperature (37°C) has to
be kept constant, within a very narrow range, in their body core, i.e. in their head and
trunk. Even a slight variation in the core temperature, an increase or decrease of just
2°C, can cause important functions within the body to fail.
The activity of the organs and muscles is constantly producing varying amounts of
heat in the body, and this "output" can be expressed in watts. To maintain a constant
temperature in the body core, the production and emission of heat by the body must be
kept in balance. This requires complex regulatory mechanisms. For example, heat is
dissipated from the body very effectively by the evaporation of sweat from the skin. In
cold conditions, the body restricts the circulation of blood to the hands and feet and so
reduces heat loss. The body can produce heat when it is cold by shivering. Because of
the large surface area of the skin, humans can dissipate more body heat through the
skin than they can by, for example, exhaling warm air.
Humans are able to adapt to different temperatures. This makes the surface of their
bodies more tolerant of temperature changes. Variations can be tolerated the least in
the trunk, where the vital organs are located. Our hands and feet, however, can put up
with downward temperature changes of 10°C or more.
How does clothing keep us warm?
It's not the textile material that clothes are made of that keeps us warm but the air that
is trapped by clothing: the purpose of clothing is to create a layer of air around the body
which serves as an insulating layer between the body and the ambient conditions. Just
like in a Thermos flask, the heat generated by the body is retained by the cushion of air
in the clothing around the body. All fibres, regardless of whether they are woollen, silk
or chemical fibres, conduct heat at least ten times better than air.
This means that what determines how warm a garment feels to us is its ability to trap
air between the fibres and stop it being exchanged with the surrounding air. In nature,
the fur on mammals and the feathers on birds work according to the same principle.
A garment not only has to offer good thermal insulation but also, depending on the area
in which it is to be used, has to be windproof, so that the insulating cushion of air is
not disturbed. Furthermore, the garment manufacture, i.e. the cut and workmanship,
also plays an important role: for example, elasticated cuffs prevent too much exchange
of air taking place as the body moves, thereby increasing the warming effect of the
clothing. On the other hand, when the body is under strain openings for ventilation
(which can be closed off), for example under the armpits, can transport excess thermal
energy away from the body through the exchange of air with the surroundings.
And what happens when we start to sweat?
Physical activity increases heat production by the body. To make sure we don't
overheat as a result, we start to sweat, even, for example, when skiing in freezing
temperatures. Excess heat is removed from the body by the evaporation of sweat on
the skin. However, for this to happen, the moisture has to be wicked away from the
body. That is why some ski suits have ventilation slits under the armpits which the
wearer can open if required. Modern membrane materials also allow the evaporated
sweat to escape outside while still offering effective protection against the rain and
If the sweat cannot be transported away from the body and dissipated into the
surrounding air, it accumulates in the layers of clothing next to the skin. This is not only
uncomfortable but, when the level of activity drops and so less heat is produced, it can
even pose a risk to health. Since water is an excellent conductor of heat, wet clothing
clinging to the body can cause people to lose a lot of heat. Together with the loss of
energy through evaporation, this can have a serious chilling effect. We can observe the
same effect in summer when the parts of the body that are covered by a wet swimsuit
become uncomfortably cold.
In what ways is modern winter clothing different from that of 50 years ago?
Right up until the 1960s, clothes were made almost exclusively of natural materials like
wool, cotton, linen, leather or fur. Admittedly, the first synthetic textile fibres had already
been developed, with `Nylon´ invented by Dr. Wallace Hume Carothers in the USA
in 1935 and `Perlon´ by Dr. Paul Schlack in Berlin in 1938. But chemical fibres really
only made their big breakthrough when scientists learned how to deliberately influence
specific desirable properties in them.
Now, by adjusting the fineness and therefore the stiffness of the fibres, and by using
special processing techniques, the volume of air that is trapped by the textile, and
consequently its thermal insulation, can be controlled and maximised. Jackets and
sleeping bags filled with fleece materials made of hollow-core fibres with excellent
lofting properties can provide a level of thermal insulation close to that of down filling.
Since the hollow filaments are relatively stiff, they cannot be easily crushed and so they
retain their warming cushion of air even under pressure.
When it comes to protection from wind and rain, membrane systems have become
well-established since they were first introduced at the end of the 1970s. The
membranes can be made of different high-tech materials: for example, the pores
of porous polytetrafluorethylene are smaller than the smallest drops of water and
so do not allow any rain to penetrate. But they are larger than a single molecule of
water vapour, so they allow sweat in the form of vapour to evaporate to the outside.
Membranes can also be made of special polyester or polyurethane which similarly do
not let water droplets in but let sweat vapour out and are effective at keeping out the
wind. A traditional oilskin jacket made of PVC- or polyurethane- (PU-)coated cotton
fabric does offer good protection from a downpour or icy winds but its breathability is
practically nil, which is why after a short time the wearer becomes soaked in his own
sweat and feels uncomfortably chilled.
In 1980, the Austrian ladies' team at the Winter Olympics in Lake Placid was
equipped with the world's first ever two-layer underwear which had been developed
in partnership with scientists at the Hohenstein Institute in Bönnigheim. Ever since,
modern functional textiles have offered both professional and amateur sportsmen and
-women clear advantages compared with traditional cotton underwear when it comes
to heat and moisture management: the synthetic fibres of the "double-face material" lie
next to the skin and conduct perspiration quickly and efficiently away from the body and
into the outer cotton layer. In combination, the two materials are far more comfortable
to wear than cotton underwear, because of the drier feeling on the skin.
Developments in this field are far from at an end. At the Hohenstein Institute, too,
researchers are constantly testing new combinations and modifications of materials to
see what the benefits are in terms of wearing comfort.
How can I judge how comfortable clothing will be to wear when I'm still in the
Even for an expert, it's hard to assess the wearing comfort of a garment just by looking
at it. The manufacturers' claims are often expressed in very flowery language, but can
be hard to compare. So anyone wanting to know which ski suit offers good thermal
insulation but won't leave you sweating buckets during the aprés-ski, or which sports
underwear will best absorb perspiration without sticking uncomfortably to their skin,
needs to rely on an objective, manufacturer-independent assessment. This is available
in the form of the wearing comfort mark, awarded by the Hohenstein Institute on the
basis of a whole series of measurements. The wearing comfort mark, generally shown
on the product together with the Hohenstein quality label, ranges from 1 for "very good"
to 6 for "unsatisfactory". It covers not only the thermophysiological properties of a
textile material, such as its thermal insulation, breathability and moisture management,
but also the skin sensory aspects of wearing comfort, that is to say, whether the textiles
feel pleasantly soft and supple or, by contrast, are uncomfortably scratchy and prone to
sticking to skin that is wet with perspiration. The Hohenstein scientists have developed
objective methods of measuring all these textile properties and the results are used to
calculate the wearing comfort mark.
Features that are optional on clothing for everyday use are already compulsory on
cold protective clothing for professional use (e.g. in cold storage warehouses): for such
clothing, manufacturers have to have the thermal insulation tested and declare the
result on the garment. Then the user can determine, from a table that is included in the
relevant standard, for how long the clothing can be worn for any given intensity of work
or ambient conditions.
What is the ideal outfit for cold weather like?
There won't be an all-round outfit that you can wear in any temperature any time soon.
However, the aim of clothing physiology research is to work out which clothing is
suitable for which purpose and area of use, and provide the wearer with information
accordingly. You can already see the results of this work in the case of sleeping bags:
a standardised process is used to calculate the temperature range in which a product
can be used without the user feeling uncomfortable or having any reason to fear
damaging their health, and this is shown on the product. For bedding, too, a system
developed by the Hohenstein Institute enables consumers to use a chart to identify the
best bedding for them, depending on the ambient temperature and the body weight of
With clothing, unlike with sleeping bags or bedding, the level of activity and the
associated varying rates of heat production by the body have to be taken into account.
Here it is still useful to apply the "onionskin principle" in cold weather, i.e. to wear
several layers of clothing on top of one another which can be removed as necessary.
When choosing them, though, you should definitely remember the issues of heat and
moisture transport described above and coordinate the different garments to achieve
the best possible heat and moisture management. After all, with the right clothing,
there's no such thing as bad weather.
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