The D'Addario Humidifier Pro protects your guitar even in the driest conditions. Using a specialized hydrophilic sponge that holds 12 times its dry weight in water (much more than an ordinary sponge), the Humidifier Pro allows for longer periods between re-fills and increases protection in drier environments. Preserving your instruments ultimate playability by guarding against cracks, warped necks, and shrinkage is now easier and less work