Grover-Trophy GP760 Acoustic Guitar Humidifier Protect your investment and it is essential to maintain a proper moisture level in your guitar. Made of soft latex which is harmless to all instrument finishes. Grover's new guitar case humidifier helps to prevent adverse effects such as bad string action. These humidifiers maintain proper humidity levels. Includes a cover to seal the sound hole during use. Easy to follow instructions and a user-friendly humidity gauge.