1、Protection Function: The humidifier pack is mainly used to protect musical instruments from warping, cracks, and other damage caused by a lack of humidity. 2、Two Way Humidity Control: This humidifier pack provides two way humidity control, and can maintain a relative humidity level of 45‑50% inside the instrument casing. 3、Automatic Regulation: Automatically maintain the optimal humidity inside the instrument casing, no manual adjustment required based on season, location, or temperature. 4、Applicable Instruments: These humidifier packs are suitable for acoustic guitar, classical guitar, electric guitar, bass, violin, cello, banjo, mandolin, ukulele, and more. 5、Convenient Use: These humidifier packs are compact and lightweight, can be placed inside the instrument casing or at the sound hole, convenient and practical. Item Type: Guitar Humidifier Packs Application: Acoustic Guitar, Classical Guitar, Electric Guitar, Bass, Violin, Cello, Banjo, Mandolin, Ukulele, and more Pack Size: Approx. 12 x 7.5cm / 4.7 x 3in 3 x Guitar Humidifier Packs 1 x English User Manual 2 x Cloth Bags