The Hornady Rechargeable Silica Desiccant Dehumidifier Canister protects your valuables against rust and corrosion. When the desiccant crystals change color, the unit can be recharged by placing it in a warm oven. Unlimited recharges ensure a lifetime of use.FeaturesFilled with rechargeable desiccantCrystals change colors when they need to be rechargedTwo convenient sizes for gun safes, cabinets, or other enclosed areasA must for humid climates