The ISO 7730:2005 standard on ergonomics in the thermal environment defines thermal comfort as the thermal sensation experienced by the human body related to its overall thermal balance. In addition, the standard takes into account the state of mind under which satisfaction with the thermal environment surrounding the individual is expressed.
User dissatisfaction or “discomfort” can be caused by heat or cold discomfort. Our body only achieves thermal comfort when there is a balance between the heat produced by the metabolism and the different ways of dissipating it. This thermal balance depends on the physical activity that the individual is involved in, the temperature, humidity, air speed and radiant temperature that surrounds them, and their clothing.
In the AITEX comfort laboratory, we analyse the different parameters that influence the thermal comfort of the user in order to prevent the clothing itself from creating situations of heat or cold stress in the individual.
PROPERTIES DEFINING THERMAL COMFORT
The requirements of a textile to ensure thermal comfort are:
- To avoid cold stress situations: good thermal insulation in cold environments to reduce body temperature loss.
- To avoid heat stress situations: good thermal conductivity and moisture transport in hot environments.
A fabric with thermoregulatory properties is a fabric that provides adequate thermal insulation combined with a proper evacuation of sweat, as it protects us from the cold and transports perspiration to the outside, keeping our skin dry.
The thermoregulatory properties of a fabric depend on the composition, weight, structure and finishes used.
According to European technical guide CEN/TR 16422:2012, which classifies the thermoregulatory properties of fabrics for use in garments, the properties that define thermal comfort in fabrics are:
- Thermal resistance.
There are two standards with which thermal resistance can be measured: ISO 11092 for the analysis of thermal resistance to convective cold and ISO 5085-1 for the analysis of thermal resistance to contact cold.
Any type of article can be analysed by either of the standards: fleeces, knitted fabrics, laminated fabrics, nonwovens, etc.
How can the thermal resistance of a material be improved?
Thermal insulation is achieved by the layers of air that are trapped within the structure of the fabric. The more air layers there are inside the material, the higher its thermal resistance.
- Resistance to water vapour and moisture transport.
This is a measure of the breathability of a material. As with the thermal resistance, any type of article can be analysed.
How can the breathability of a material be improved?
By using light, open-structure fabrics and materials with good air permeability and resistance to water penetration.
- Air permeability.
Depending on the intended use of the material, either high air permeability or low air permeability is required.
Air permeability will depend on the structure of the fabric or the finish used in its manufacture.
- Resistance to water penetration and repellence.
These tests measure the properties of waterproof garments, an important factor in the thermal comfort of the user in situations of heavy or moderate rain.