The D Addario Humidipak Maintain is the only maintenance-free two-way humidity control system for the guitar. It automatically maintains the optimal 45 to 50 percent 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 that 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 or case will greatly shorten the lifespan of the packets. It is ideal for instrument care and maintenance acoustic guitars and acoustic-electric guitars.