Desiccant refers to a substance that can remove moisture from moist materials. It is often divided into two categories: chemical desiccants, such as calcium sulfate and desiccant calcium chloride, which are dried by combining with water to form hydrates. The use of super dry desiccant is to avoid the occurrence of defective products caused by excess moisture. Thehumidity control packet automatically protects your wooden instrument from warpage, cracks and other damage caused by insufficient humidification or excessive humidification. Maintain a constant 50% relative humidity level with the instrument (closed). Unlike all other unidirectional humidifiers, the guitar humidity control packet is the only true two-way humidity control that can add or remove moisture as needed to maintain 50% relative humidity in the guitar case.