D’Addario Two-Way Humidification System® replacement packets make ongoing humidity control for your guitar easy. Depending on climate conditions, a packet may last from two to six months. When the contents of the packets become solid, it’s time to replace them. Simply discard the old ones and slip the new packets into the soundhole and headstock pouches that come with the complete kit. The packets take care of the rest, providing two-way humidity control that either absorbs or adds moisture to maintain a constant relative humidity of 45-50 percent. Model# 80357