The D'Addario Two-way Humidification Replacement Pak lets you maintain a constant 45% humidity level for your instrument. The Two-way Humidification Replacement Pak keeps a steady humidity level by adding or depleting moisture as necessary. Now you can keep your prized instrument stored without having to resort to messy, refillable units. Protect your investment with the D'Addario Two-way Humidification Replacement Pak.