The Boveda humidity system is a new technology with a simple idea - a product that maintains a constant humidity level in your case. Designed to both remove and replace moisture for your instrument, the Boveda system starter kit comes with a small cloth bag to hold the packet. Simply put it in your case and it will maintain a constant 49% humidity. The starter kit comes with 2 packs which typically last 6 months each. Replacement packs are also available.