Features:
Designed for acoustic guitar with 99-101mm sound hole diameter.
Used as a guitar humidifier, simply moisten the included sponge and install for reusable humidification.
Working as a guitar dehumidifier, using the included desiccant to absorb moisture around your guitar.
Can also be used as a normal sound hole cover to eliminate unwanted feedback.
Soft rubber covers the insert edge, no damage to your guitar.