Our transformer desiccant breathers are constructed of very durable materials. The small units are made from a tough UV stabilized glass loaded polycarbonate. The larger units are constructed from aluminum. All units are fitted with a two-way relief valve mechanism that eliminates all maintenance except for replacing the desiccant once it is saturated. All the breathers have a viewing window (there is 180-degree visibility on the small units) to easily determine when the desiccant needs to be replaced.