• Humidification system: D'Addario's Humidipak is the only maintenance-free two-way humidity control system for guitar. It includes humidifier bags and packs for guitar. • Protect your guitar: Protects your instrument against warping, cracking, and other damage caused by lack of humidification. • Two-way humidity control: The first two-way humidity control that maintains a constant relative humidity level of 45% to 50% inside your instrument's case. • Automatic humidifier: Automatically maintains the optimal relative humidity level of 45%-50% inside your instrument's case, eliminating guesswork and the potential mess associated with refilling a humidifier. • Automatic adjustments: No more manual adjustments based on seasonal changes, geographic locations, temperature, or other factors, unlike refillable humidifiers.