D'Addario brings you Boveda's patented technology as part of our instrument care line. The Two-Way Humidification System (formerly 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, this 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 Two-Way Humidification System comes with 3 Humidipaks and a soft mesh pouch that will not harm your instrument's finish. These packets last between 2 and 6 months and should always be kept in a sealed environment like a hard-shell case. Once the packets become firm, discard and replace using the 3 refills that come in the D'Addario Two-Way Humidification Replacement Pack (PW-HPRP-03). This all new, reformulated, patented two-way humidification system maintains 45-50% relative humidity which eliminates all maintenance and guesswork. This system is recommended by taylor guitars and others for maintaining the stability and playability of your instrument.