The skin formation time refers to the time in which a “solid” skin forms on the adhesive. This term is mainly used for adhesives that react with humidity from the outside to the inside. During this period, the surface of the coating begins to air dry, forming a skin.

The length of skin formation time depends on various factors, such as the type of coating, ambient temperature, relative humidity and air movement. As a rule, the skin formation time is specified by specifying a dry film thickness and a time, for example "2 hours at 20°C and 50% relative humidity". Accurate determination of skin formation time is important as it impacts the overall drying time and adhesion of the coating.

If the skin formation occurs too quickly, this can lead to cracks or unevenness on the surface, while a skin formation time that is too long can impair adhesion and increase the overall drying time. If the skin formation has already progressed too far before joining, the wetting of the second part to be joined will be difficult or may no longer take place. The joining must therefore be completed before the skin formation time has expired.

Colloquially, not entirely chemically correct, skin formation time is also sometimes used as a synonym for open time, pot life and processing time.