Cleanroom classes are a classification of cleanrooms according to the degree of cleanliness of the air, which is determined by the maximum permissible particle concentration and particle size. The cleanroom classes are defined in various standards and guidelines, such as DIN EN ISO 14644-1 or the EC GMP guidelines. Depending on the area of application and industry, different requirements apply to the cleanroom classes. The cleanroom classes range from ISO 1 to ISO 9 or from A to D, with the lowest number or the first letter indicating the highest cleanliness.