Condensation on glass windows and other surfaces caused by the emission of substances from leather, Imitation leather or plastic is known as fogging. When exposed to higher temperatures, these substances evaporate from the leather and plastic materials used in the vehicle's interior and remain on the car windows, which are cooled from the outside. The resulting condensation affects the visibility through the window.
When investigating fogging behaviour of leather, emission values of various substances are tested under a wide variety of circumstances (VOC emission investigations). Various chemicals are also used in the tanning process which can subsequently lead to fogging. It is also important to dry the leather sufficiently.
In these tests, a leather is heated to speed up the effect. Triggers for fogging can be excess fats, ammonium salts or softeners.
In 2015 the Deutsche Gütegemeinschaft Möbel DGM (German furniture quality assurance association) launched an emission label for furniture. The label includes leather furniture and leather care.