EN ISO 11092 EN ISO 11092 Textiles - Physiological Effects - Measurement of Thermal and Water Vapor Resistance under Steady-State Conditions (Hot Plate Test with Sweat Protection)

The basic standard “EN ISO 11092 Textiles - Physiological effects - Measurement of thermal and water vapour resistance under steady-state conditions (hot plate test with perspiration protection)”, developed by the British Standards Institution (BSI) and published by the International Standards Organisation (ISO), describes a procedure for measuring thermal resistance and water vapour resistance under steady-state conditions for use in clothing, duvets, sleeping bags, upholstery and textile-like products, including multi-layer assemblies such as fabrics, films, coatings, foams and leather.

The application of this measurement technique is limited by the maximum thermal resistance and water vapour resistance, which depend on the dimensions and construction of the device used (for example, the minimum characteristics of the equipment specified in this standard are 2 m2 K/W and 700 m2 Pa/W, respectively).

The test conditions used in this international standard are not intended to represent specific comfort situations, and performance characteristics related to physiological comfort are not specified.

For the purposes of this standard, the following terms and definitions apply:

• Thermal resistance is the value calculated by dividing the temperature difference between two surfaces of a material by the resulting heat flux per unit area in the direction of the gradient. Thermal resistance is a quantity specific to textile materials or composites that determines the dry heat flux in response to a constant applied temperature gradient across a given area. The dry heat flux may consist of one or more conductive, convective and radiant components. Thermal resistance is expressed in square meters kelvins per watt.
• Water vapor resistance is the value calculated by dividing the water vapor pressure difference between two surfaces of a material by the resulting evaporative heat flux per unit area in the direction of the gradient. Water vapor resistance is a quantity specific to textile materials or composites that determines the latent evaporative heat flux in response to a constant applied water vapor pressure gradient across a given area. Evaporative heat flux may consist of both diffusive and convective components. Water vapor resistance is expressed in square meter pascals/watt.
• The water vapor permeability index expresses the ratio of thermal and water vapor resistances according to the formula given in the standard. The water vapor permeability index is dimensionless and has values ​​between 0 and 1. A value of 0 indicates that the material is impermeable to water vapor, i.e. has infinite water vapor resistance, and a material with a value of 1 has both the thermal resistance and water vapor resistance of an air layer of the same thickness.
• Water vapour permeability is the characteristic of a textile material or composite depending on its resistance to water vapour and temperature according to the formula given in the standard. Water vapour permeability is expressed in grams per square metre hour pascal.

When testing, in principle, the sample to be tested is placed on an electrically heated plate with conditioned air channels to flow parallel and crosswise to its upper surface as specified in this standard.

To determine thermal resistance, the heat flux through the test sample is measured after steady-state conditions are reached.

This technique allows the thermal resistance of a material to be determined by subtracting the thermal resistance of the boundary air layer above the surface of the test device from the thermal resistance of a test specimen and the boundary air layer measured under the same conditions.

To determine the water vapor resistance, an electrically heated porous plate is covered with a membrane that is permeable to water vapor but impermeable to liquid water. Water fed to the heated plate evaporates and passes through the membrane as vapor, so that liquid water does not contact the test sample. When the test sample is placed on the membrane, the heat flux required to maintain a constant temperature in the plate is a measure of the rate of evaporation of water, and from this the water vapor resistance of the test sample is determined.

The measuring unit with temperature and water supply control consists of a metal plate with a thickness of about 3 mm and a minimum area of ​​0,04 m2 (for example, a square with a length of 200 mm on each side) fixed to a conductive metal block containing an electric heating element. For measuring water vapor resistance, the metal plate must be porous. This device is surrounded by a thermal guard located in an opening in a measuring table.

Among the numerous tests, measurements, analyses and evaluation studies that our organization has carried out for businesses in various sectors, our organization also provides testing services defined in the standard “EN ISO 11092 Textiles - Physiological effects - Measurement of thermal and water vapor resistance under steady-state conditions (hot plate test with sweat protection)” with its trained and expert staff and advanced technological equipment.