Planet Waves GH-RS replacement sponges for the GH Series humidifier. For extending the life of your instrument and enhancing its tone. Proper humidity levels prolong the life of your guitar, and also make it sound its best. The Planet Waves GH Series humidifier is suspended by the strings, so it never touches your instrument - and the leak-resistent open-cell foam releases moisture slowly and evenly. Want the best performance out of your guitar? Use the Planet Waves GH Series humidifier, and get these GH-RS replacement sponges to make sure you always have one handy.