The Ukulele Humidifier Pro is D 'Addario's first ukulele humidifier designed to fit in the sound hole of the instrument. Based on the design of the Guitar Humidifier Pro, this version contains an easy-to-remove rubber cap and a hydrophilic sponge in a much smaller size that is perfect for a ukulele. The hydrophilic sponge holds up to 12x its own weight in water, which means it will hydrate the instrument over a longer period of time. D 'Addario is known for innovative, problem-solving, quality musical products with a complete line of award-winning accessories including cables, picks, tuners, capos, straps, humidifiers, maintenance tools and more.