The D'Addario PW-SIH-01 Small Instrument Humidifier protects your instrument even in the driest conditions against cracks, warping, and shrinkage. The humidifier releases moisture evenly and slowly inside your instrument case to maintain the proper humidity level. Maintaining the humidifier is as easy as moistening the sponge when it becomes dry. The frequency of maintenance can vary depending on your specific atmospheric conditions. asy to use! The Planet Waves Small Instrument Humidifier is easy to use and is ideal for smaller acoustic, bowed, and woodwind instruments.