This document specifies the construction and performance of actively heated suits and actively cooled suits for wear by divers for underwater activities where the user is breathing underwater. Marking, labelling, information to be provided at the point of sale, and instructions for use are also specified. The document applies to the actively heated or cooled suits (systems) of the two types, dry and wet. It is only required that the suit should fulfil this part 3, not the parts 1 or 2 unless specified. Laboratory and practical performance tests are specified.