ISO-rated cleanroom supplies are low shedding to prevent particles from contaminating the environment. They're assigned a cleanroom class to indicate which cleanrooms they can be used in. Lower classes (ISO 1) indicate cleaner equipment than higher numbers (ISO 9), so rating with a lower number can be used in cleanrooms with a higher number. For example ISO 1-rated equipment can be used in ISO 1 to ISO 9 cleanrooms, and ISO 4-rated equipment can be used in ISO 4 to ISO 9 cleanrooms.