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Seat comfort usually means the ergonomic comfort, i.e. the mechanical support the seat gives to the body. However, likewise important is the thermo-physiological comfort, i.e. the seat's ability to control the heat and moisture transport from the body. If this climatic comfort is missing, the performances of the driver are considerably impaired. In order to create a car seat with a good thermo-physiological function, it is necessary that during the product development seat comfort can be quantitatively measured and assed. One appropriate instrument is controlled seat trials with human subjects in a climatic chamber, in which certain temperature, humidity and air movement conditions can be fixed. With the upholstery tester, entire car seats can be tested. Its main part is an 'indentor', an aluminium stamp with a rotational elliptical shape which simulates the contours of the human body. The skin model is a thermo-regulating model of the sweating human skin. The car seat specimen is placed on the skin model and loaded by lead weights with 14.7 cN/sqcm, simulating the static pressure a person exerts on the seat. With the skin model a normal situation with moderate sweating can be simulated, with a steady amount of water vapour. Increased sweating is simulated by suddenly evaporating a defined amount of water. Measurements of the water vapour resistance with the skin model as well as the results of controlled seat trials with human subjects reveal that with regard to breathability and moisture management within the microclimate next to the body spring cores or rubberised hair pads perform better than foam pads. The ventilation, and thus the heat and moisture transport of the seat, can be optimised by a forced air stream created by a built-in fan in a ventilation layer, which is made from a knitted synthetic spacer fabric with a thickness of about 10 mm. In order to prevent the penetration of the forced air stream through the lining and covering fabric, the upper side of the ventilation layer is covered by an air-tight membrane, which is water vapour permeable. The transfer of physiological principles into a car seat demands a certain production price, which sometimes exceeds the cost frame allotted to the seat.