The Humidifier Pro protects your guitar even in the driest conditions. Using a specialized hydrophilic sponge that holds 12x its dry weight in water (much more than an ordinary sponge), it allows for longer periods between re-fills and increases protection in drier environments. Suspended by the strings, the humidifier releases moisture evenly and slowly inside your guitar, without touching the guitar's body. Maintaining the humidifier is as easy as moistening the sponge when it becomes dry and the humidifier's stopper allows you to check the sponge status without removal of the unit and provides a tight seal when in place.