The Ukulele Humidifier Pro is designed to fit in the soundhole of a ukulele. Based on the design of D'Addario's Guitar Humidifier Pro, this humidifier contains an easy-to-remove rubber cap and a hydrophilic sponge in a smaller size that is perfect for a uke. The humidifier's stopper provides a tight seal when in place and allows you to check the sponge status without removal of the unit. The specialized sponge holds 12 times its dry weight in water, far more than an ordinary sponge, which allows for longer periods between refills as well as increasing protection in drier environments. Suspended by the strings, the humidifier releases moisture evenly and slowly inside your ukulele, yet never touches the instrument's body.