The Two-Way Humidification System (formerly Humidipak) takes the stress and the guesswork out of guitar humidification. The Two-Way System will both authomatically release moisture during the dry months as well as take in excess moisture in more humid months, making it the perfect companion for your acoustic guitar year round. The system kit includes 2 mesh pouches, and two Humidipak packets. One pouch will accept one packet and should be placed underneath the headstock inside of your guitars case. The other pouch will hold two packets and should be draped down over the strings into the soundhole when the guitar is not being played. When used correctly and consistently, the the system will keep your guitar at the optimal 45-50% relative humidity, the exact range specified by high end manufacturers as the proper conditions for an acoustic guitar. The kit itself will last from 2-6 months, depending on specific climate and replacing the packets is as easy as throwing away the used, hardened packets and replacing them with a fresh set from the D'Addario Two-Way Humidification Replacement Pack.