Skin sensorial comfort vote

In order for the skin sensorial comfort vote to be calculated, textiles have to go through seven tests which provide information about both their skin sensory and their thermophysiological characteristics.

Parameters for skin sensory testing:
1. Stiffness

The stiffness of a textile material is measured in a special device by using a laser beam to calculate the bending angle of a sample strip draped over a thin stick. Based on their many years of experience, the scientists at the Hohenstein Institute have defined the criteria for different products and areas of use which ensure maximum wearing comfort and prevent any mechanical skin irritation caused by excessive stiffness.

2. Sorption index

As skin becomes more moist, it becomes more sensitive to mechanical irritation. That is why it is important for a textile material to transport sweat away from the skin as quickly as possible. The sorption index indicates the speed at which a drop of water on the textile is absorbed by it. To measure this, a drop of water is applied to the textile sample and observed by a video camera. The angle of contact between the drop of water and the surface of the textile is measured continuously to establish how quickly the material absorbs liquid sweat.

3. Surface index

The surface index describes the smoothness or hairiness of a textile. Here, a camera records an image of a cross-section of the textile. Scientists then calculate the number and size of the protruding fibres in the fabric. The surface index can be used to judge, for example, whether a textile will scratch or feel too smooth.

4. Number of contact points

Image-analysis systems connected to a surface scanner show the number of contact points and the surface structure of textiles. These can be used as a scale for working out what area of the textile material is in contact with the skin. Over their decades of research the Hohenstein scientists have developed guidelines for the optimum number of contact points for textiles.

5. Wet cling index

Water is applied to a sintered glass plate to simulate sweating skin. The textile sample is secured and drawn over the plate. Measuring the force required to do this produces the wet cling index, from which it can be judged whether the textile will stick to the skin and feel uncomfortable when you sweat.

We conduct our laboratory testing of skin sensory functions using test equipment we have developed inhouse, and in compliance with accredited test regulations.

Thermophysiological testing:

Because both dry and moist heat emitted by the skin affect skin sensory perception, thermophysiological measurements also form part of what are primarily skin sensory measurements.

6. Water vapour resistance

The Hohenstein Institute measures water vapour resistance using the Skin Model in a climate-controlled cabinet. This simulates the flow of moist heat from the skin in the form of insensible sweating. The textile being tested is placed on a hotplate and water is passed through the "pores" of the hotplate. A process of evaporation creates water vapour and, depending on the "breathability" of the textile, this is transported away from the plate. The key factor in the measuring process is the energy that is required to keep the temperature of the Skin Model constant and create water vapour. The data is used to measure the water vapour resistance and determine the level of "breathability".

7. Thermal insulation

This test measures how well a textile retains the heat emitted by the body. The Skin Model simulates the flow of dry heat from the skin, the heat that is given off. During the measuring process, the hotplate is set at a higher temperature than the ambient surroundings. Consequently, the plate cools down at a rate determined by the thermal insulation properties of the textile. To maintain a constant temperature, the metal plate is heated by an energy supply. The measurements can be used to calculate the thermal insulation of the test sample.

In our thermophysiological testing, we use the Skin Model. This simulates the way the skin gives off heat and sweat. The test takes place under standardised conditions in a defined test environment inside a climate-controlled cabinet, in compliance with DIN EN 31092/ ISO 11092.

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