OPTIMAL RELATIVE HUMIDITY (RH) LEVELS Relative Humidity (RH) Level Recommended Items 50%–60% Books, antique documents, paper (fax, copy, print) 40%–50% Camcorders, cameras, lenses, telescopes, microscopes, endoscopes, compact discs, film negatives, film transparency/slides, microfilm, disk drives, audio and video tapes 35%–40% Metal and metal powder products, electrical equipment, semiconductors, capacitors, printed circuit boards, IC, batteries and other electronic equipment, precision measuring too