The 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. Unlike refillable humidifiers, the Humidipak system provides true ?two-way? purified humidity control by adding and removing moisture on demand. No more manual adjustments based on seasonal changes, geographic locations, temperature, or other factors. The Humidipak Kit comes with 3 Humidipaks and a soft mesh pouch that will not harm your instrument's finish. Humidipaks last between 2 and 6 months and should always be kept in a sealed environment like a hard-shell case. Once the Humidipaks become firm, discard and replace using the 3 refills that come in the Planet Waves Humidipak Replacement Pack (PW-HPRP-03). D'Addario is known for innovative, problem-solving, quality musical accessories. D'Addario offers a complete line of award-winning accessories including cables, picks, tuners, capos, straps, humidifiers, maintenance tools and more