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The quest for greater comfort clothing and body climate

The Hohenstein Institute’s Dr. Andreas Schmidt explains the fundamentals of clothing and body climate and the objective measurement of comfort. He then goes on to discuss the birth and the state of the art of functional textiles. 4 January 2011, Bönnigheim - People have always been interested in the connection between clothing and physical well-being. The scientific discipline of clothing physiology, on the other hand, which in Germany has been shaped primarily by the Hohenstein Institute in

4th January 2011

Innovation in Textiles
 | 

Sports/​Outdoor, Medical/Hygiene, Clothing/​Footwear

Dr Andreas Schmidt, Hohenstein InstituteThe Hohenstein Institute’s Dr. Andreas Schmidt explains the fundamentals of clothing and body climate and the objective measurement of comfort. He then goes on to discuss the birth and the state of the art of functional textiles.

People have always been interested in the connection between clothing and physical well-being. The scientific discipline of clothing physiology, on the other hand, which in Germany has been shaped primarily by the Hohenstein Institute in Bönnigheim since 1946, is comparatively young.

One of the main aims of the science is the systematic design of functional clothing which does as much as it can to help regulate the temperature of the human body, in relation to the ambient temperature and the level of physical activity. Critical factors in this are the thermal insulation and moisture management properties of textile materials, i.e. their ability to absorb perspiration and wick it away from the body.

Sweating is essential for our survival

Sweating is the most effective way the human body has of cooling down. It takes a lot of energy to evaporate the sweat and this is taken from the skin in the form of heat. Every litre of sweat takes about 580 kcal – that equates roughly to the calories burned up during one hour of intensive fitness training, or the calorie content of a fast-food meal. The evaporation of sweat is also the only way for the body to lose heat where the outside temperature is higher than body temperature. The most effective cooling is achieved by sweat evaporating directly on the skin.

The ability of a textile to transport perspiration in the form of vapour through itself and out to the exterior is generally referred to as its breathability. It is incorrect to use the terms breathability (or resistance to water vapour) and air permeability interchangeably, because low air permeability does not in itself result in lower breathability. The best example of this is modern wind- and waterproof membranes, which allow very little air to permeate in from outside (windproof), but still allow evaporated perspiration to pass through from the inside.

However, breathability is only one aspect of heat and moisture management – what are called the thermo-physiological characteristics. It is also important that the liquid sweat is absorbed, stored and then transported away in sufficient quantities that someone wearing the garment feels, literally, "comfortable in their skin".

Comfort can be measured objectively

The Hohenstein skin model consists of a porous sintered metal plate which is used to simulate the formation of heat and moisture in human skin. Pictures: Hohenstein InstituteBoth thermo-physiological comfort and skin sensory comfort (i.e. how textiles feel on the skin) can be objectively measured and evaluated in the laboratory. At the Hohenstein Institute, a number of test methods have been developed since the 1950s which are now used around the world.

The skin model simulates the way heat and moisture are emitted from the skin. It consists of a sintered, porous metal plate that can be warmed electrically to skin temperature and to which water is supplied. It is located in a climate chamber, where permanently stable measuring conditions can be maintained.

For textiles, measurements taken using the skin model supply specific parameters such as, for example, thermal insulation and resistance to water vapour permeability, as a measure for breathability", perspiration transport and buffering, drying time, etc. These parameters characterise the thermo-physiological quality of textile materials.

One of the ways researchers at the Hohenstein Institute assess the comfort of sportswear is by using the thermal articulated manikin, Charlie. Picture: Hohenstein InstituteWith the help of the thermal articulated manikins 'Charlie' and 'Charlene', also developed at the Hohenstein Institute, the thermal insulation properties of manufactured garments, bedding and sleeping bags can be calculated. Using what are known as human thermoregulation models, the heat generated by adults and children can be simulated.

The articulated manikins are made of copper or synthetic materials and have been fitted with a computer-controlled heating system that allows the heat generation for different parts of the body to be regulated separately. The more heat emitted from the arms or legs, for example, the worse the thermal insulation of the garment is for those areas of the body.

This is very significantly influenced by any exchange of air between the clothing and the outside when the body is in motion, for example at the cuffs or fastenings (ventilation effect). That is why the articulated manikin 'Charlie' is set up on a stand when clothing is being tested, as if he were out for a brisk walk. The assessments made using the thermal articulated manikins are an important supplement to the evaluation of moisture management that is carried out using the skin model.

In the "sweating foot" thermo-regulation model, the functional principles of the Hohenstein skin model and the thermal articulated manikins have been combined. That is to say, it emits both moisture and heat, and is in the shape of a typical foot.

This means that, for the first time, it is possible realistically to simulate the thermal conditions at the body's extremities. It is important to realise that, when the ambient temperature is low, far more heat is lost from the toes, where the surface area islarge in proportion to the mass, than, for example, from the back.

This means that, to maintain a comfortable skin temperature, the thermal insulation of socks and shoes has to be that much higher. At the same time, treated textile materials have to be able to absorb the sweat that is produced, especially during physical activity, very effectively, and wick it away from the body.

The birth of functional textiles

The development of the first synthetic textile fibres 'Nylon' and 'Perlon' in the 1930s marked the start of a new era in textiles: alongside the traditional natural fibres, there were for the first time also new materials available, the properties of which could be deliberately controlled.

Of course, in the 1960s, the catastrophically uncomfortable so-called Nyltest shirts gave synthetic fibres a bad name. Nevertheless, tests by the Hohenstein Institute over subsequent years showed that, if textiles made from synthetic fibres were properly designed, they could not only offer the same heat and moisture management qualities as natural fibres but even exceed them.

It was on the basis of research carried out at Hohenstein that, at the start of the 1980s, the first two-layer ('double face') textiles were produced, where layers of natural and synthetic fibres were combined, yet kept separate. The synthetic fibres of the "double face material" were next to the skin and conducted perspiration quickly and efficiently away from the body and into the outer cotton layer.

In combination, the two materials were far more comfortable than cotton, because of the drier feeling on the skin. In 1980, a sportswear manufacturer equipped the Austrian ladies' team at the Winter Olympics in Lake Placid with two-layer underwear, which was subsequently also made available to amateur athletes under the trade-name 'Transtex'. With its enormous success on the market, functional textiles began a triumphal march which continues to this day and is leading to ever greater differentiation between materials, depending on their intended purpose.

The state of the art

If their clothing is going to enable amateur and professional sportsmen and women to perform at their best, it must be able to help regulate body temperature in relation to the ambient conditions and the level of activity. Picture: Oeko-Tex.At the Hohenstein Institute, researchers are constantly testing new combinations and modifications of materials to see what the benefits are in terms of comfort. Instead of cotton, double-face materials nowadays use modern regenerated fibres as the outer layer.

However, the trend is clearly in the direction of innovative fabric structures and modifications to the profile and fineness of the fibre, in order to make the surface of the fibre more efficient and maximise the transportation of liquid sweat.

A gradual variation in the fineness of the fibres and yarns from the inner surface of the textile to the outer surface also improves moisture management; because the resulting narrowing of the capillaries (denier gradient) means that the moisture can be transported away from the skin really effectively.

Any further improvements to the level of comfort resulting from fibres and fabrics will most likely now only be made in the detail - because of the high standard that has already been reached, quantum leaps can only be expected in exceptional cases.

The most promising area for future development probably lies in combining the specific strengths of synthetic, regenerated and natural fibres. There is a great deal of potential for development in integrating electrical and electronic components such as heating or cooling elements. The latest battery technology and innovative methods of processing and wiring, including the use of conductive textiles or solar panels, all open up new areas of use and, above all, it will become easier to wash the complete outfit.

Top marks for comfort

The comfort of sportswear can be measured and assessed objectively, but this does require the tests referred to above to be carried out. The physiological properties of textile materials cannot be judged by their appearance or feel, even by an expert. This is why it is difficult or impossible for even experienced specialist retailers to test whether there is any scientific substance behind the extravagant claims of manufacturers.

A comfort rating offers guidance and a way of comparing different products. As well as the thermo-physiological properties, it also includes an assessment of the skin sensory properties of a textile material, i.e. how it feels on the skin.

Skin sensory parameters such as bending strength, or the number of contact points, can also be measured objectively in the laboratory by means of a series of tests. The parameters and their weightings are adapted depending on the type of textile - for example, different formulae are used for sportswear than for everyday clothing.

The level of comfort is rated using the German school marks system, from 1 for "very good" to 6 for "unsatisfactory". Many manufacturers apply this comfort rating to their retail products in the form of the Hohenstein quality label and this enables specialist retailers to compare different products easily.

Sales arguments for sports retailers

Sportswear with a high comfort rating gives a long-lasting boost to the wearer's physiological performance. Modern materials and combinations of materials enable their functionality to be perfectly aligned with the requirements of different areas of use, and adapted to suit an athlete's individual constitution. Advice on this can only be provided by experienced sports retailers, who have expert knowledge of the interplay between clothing and body climate.

Some of the features that make sportswear really comfortable:

  • high breathability (= low resistance to water vapour) e.g. for outdoor jackets - Ret<13 m2 Pa W-1, or for sports T-Shirts Ret<5 m2 Pa W-1
  • quick drying
  • high moisture transport capability
  • good wettability
  • good skin sensory qualities (how it feels on the skin) = comfort rating 2 (good) or better
  • scientifically based advertising claims
  • physiological properties checked and tested by an independent institute
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