3 replacement packs for the D'Addario Humidipak system. Automatic humidity control protects your instrument against warping, cracks and other damage cause by lack of humidification. No more manual adjustments based on seasonal changes, geographic locations, temperature, or other factors Unlike refillable humidifiers. Eliminates the guesswork and anxiety of maintaining your instrument’s proper humidity level. Learn more and view FAQ's at http://www.accessories.daddario.com/PWFAQ.Page?solutionid=469.