The first two-way humidity control that maintains a constant 45%-50% relative humidity level within your instruments case. Protects your instrument against warping, cracks and other damage cause by lack of humidification. No more manual adjustments based on seasonal changes, geographic locations, temperature, or other factors Unlike refillable humidifiers. Eliminates the guesswork and anxiety of maintaining your instrument’s proper humidity level. No water, no drips, no mess. Custom made by Boveda for D'Addario. • MFSKU PW-HPK-01 • UPC 019954952907