D'Addario Humidipak is the only maintenance-free, two-way humidity control system for guitar. It automatically maintains the optimal 45%-50% relative humidity level within your instrument case, eliminating the guesswork and potential mess related to refilling a humidifier. No more manual adjustments based on seasonal changes, geographic locations, temperature, or other factors. Note: Humidipak is designed for restoring and maintaining instrument humidity. This product is not intended for dehumidification in high humidity environments. If Your instrument has not been previously humidified or is in a known dry condition, it is recommended to use Humidipak Restore to safely reestablish the proper humidity level to your instrument and its case before using the Humidipak Maintain System. Using Maintain packets on a dry instrument / case will greatly shorten the lifespan of the packets.