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 Humidipak Replacement Pack (PW-HPRP-03). D'Addario is known for innovative, problem-solving, quality musical accessories, offering a complete line of award-winning accessories including cables, picks, tuners, capos, straps, humidifiers, maintenance tools and more. The first two-way humidity control that maintains a constant 45%-50% relative humidity level within your instruments case. Protects your instrument against warping, cracks and other damage cause by lack of humidification. No more manual adjustments based on seasonal changes, geographic locations, temperature, or other factors Unlike refillable humidifiers. Eliminates the guesswork and anxiety of maintaining your instrument’s proper humidity level. Humiditrak™ works on the following Apple iOS devices with Bluetooth™ 4.0 (iOS 7 or greater required): iPhone 4s and higher, iPad Mini, iPad 3rd and 4th generation, iPad Air and iPod Touch 5th generation. The Humiditrak app is available as a free download. Future iOS devices will be supported as they become available. Humiditrak is also compatible with all Android devices supporting version 5.0 or higher and Bluetooth Low Energy.