The main purposes of functional clothing are to provide protection from climatic influences and to support the physiological functioning of the human body. This is particularly important for the uniforms of members of the armed forces; even at temperate latitudes, soldiers are exposed to widely varying ambient temperatures and at the same time the degree of physical strain caused by their activities also varies greatly. Functional uniform systems have to cater for these extremes and ensure that the soldiers can still perform well in every situation. In short, they have to be very comfortable for their wearers.
Soldiers don’t need every comfort – or do they?
In common parlance, the word comfort can sometimes be used to mean convenience, or even luxury, which depends on the presence of certain appliances, objects or fittings. However, from a physiological point of view, the term has a much more fundamental meaning; it means the absence of factors which could have a distracting or disagreeable effect on the wearer, or even be damaging to their health.
It is also known from sports science that performance can be markedly improved by wearing clothing that provides a high degree of physiological comfort. Discomfort, on the other hand, correlates directly with a deterioration in concentration and condition, symptoms of physical breakdown, lasting damage to health and even death. Simply the uncomfortable sensation on the skin of scratchy or stiff material can be distracting and reduce the willingness of the wearer to accept the uniform.
Inadequate physiological comfort and its consequences
In combat, even slightly impaired concentration or physical condition can be an extraneous influence with fatal consequences. If clothing is not entirely appropriate to the ambient climatic conditions and to the nature of the physical activity, the resulting inadequate physiological comfort can also have serious implications for the performance and health of the soldiers.
Possible consequences range from loss of fine motor skills to heat cramps and often lead to temporary or even permanent incapacity for work.
Indeed, in the drive to make troops ready for action, able to concentrate and perform well, the human constitution is the weakest link. Modernising the technical equipment and even making uniforms more functional are pointless unless the level of comfort is similarly improved.
How can functional clothing help with thermoregulation?
Clothing which is very comfortable physiologically is particularly effective in helping with its wearer’s thermoregulation. This term covers all the physiological processes which help the body to maintain a constant core temperature of about 37°C. That includes, for example, sweating when you are hot or the way blood vessels retreat from the skin when you are cold.
There are numerous design parameters that determine the features of clothing relating to physiological comfort. The thermal insulation properties of textiles, and their capacity to transport away the body’s sweat, can be effectively controlled by the types of fibres that are used and the thickness, finish, weave and pore size of the textiles.
When the ambient temperature is low and the wearer is carrying out moderate physical activity, their clothing should possess good thermal insulation properties and be breathable so that sweat can be effectively released into the surrounding atmosphere in the form of vapour. Where the wearer sweats more heavily due to higher ambient temperatures and/or increased activity, the material must also be able to act as a buffer for more sweat (in liquid or vapour form). Large quantities of sweat caused by high ambient temperatures and/or physical activity must be efficiently absorbed and transported away from the body. The clothing must also dry quickly so as to prevent the wearer becoming cold during rest periods.
However, in addition to the (thermo-)physiological features of the textiles, the way they feel on the skin, the so-called skin sensory properties, should not be overlooked. For example, textiles that are too smooth, that stick to the skin, can feel just as uncomfortable as materials that are too scratchy or stiff.
How can the level of comfort of uniforms be objectively evaluated and improved?
There are a number of internationally recognised test methods which can be used to evaluate the physiological properties, i.e. the heat and moisture management of textiles and manufactured garments, objectively and cheaply. The majority of these were developed by scientists at the Hohenstein Institute in Bönnigheim (Germany). The measurements that are produced go towards assigning what is called the ‘comfort mark’ one of the elements shown on the Hohenstein quality label.
The skin model simulates the way human skin produces heat. It consists of a porous sintered metal plate which is heated electrically and uses a water supply system to simulate the release of sweat at different levels of intensity, as described above. To ensure that the measurements are accurate and reproducible, the skin model is housed in a climate chamber. This makes it possible to measure not only the thermal insulation but also the water vapour permeability (breathability), sweat buffering, sweat transportation and drying times, i.e. all the properties required in functional textiles.
The skin sensory features of textiles can also be objectively assessed in the laboratory. The different ways in which people experience contact with a textile are reflected using five different indices:
- The sticking index shows how much a textile sticks to skin that is damp with sweat
- The wetting index measures time and the angle of contact to provide information about how quickly a drop of water is absorbed by the textile
- The surface finish index shows whether a textile is hairy or smooth
- The number of contact points between the textile and the skin show how quickly a textile will feel damp and clammy
- The stiffness measurement is important for how well the textile product fits the body
Awarding marks for comfort – how does it work?
Putting together and interpreting all the measurements is not easy. Based on the findings from extensive wear trials, all the different parameters contribute to producing a mark for the level of comfort. Like the system used in German schools, the marks range from 1 (= very good) to 6 (= unsatisfactory) and provide a quantitative assessment of the physiological quality of a textile product.
During the product development process, the scientists at the Hohenstein Institute define a specific requirements profile described in terms of the thermophysiological and skin sensory factors for textiles, taking account of the conditions in which they are to be used. This kind of expertise is unique in the world and the result of decades of research work.