Humidifier for Acoustic Instruments with leak-resistant open-cell foam that releases moisture slowly and evenly. An acoustic guitar sounds its best when the body has just the right amount of humidity. Proper humidity levels can not only make your guitar sound it's best, but also prolong the life of your instrument. Suspended by the strings (without touching the instrument), the humidifier contains leak-resistant open-cell foam that releases moisture slowly and evenly inside the guitar. Maintain the sound quality of your precious acoustic instrument with the Planet Waves Guitar Humidifier.