Mold is a live fungus that gets its food by dissolving food materials with secreted digestive enzymes. Mold is naturally attracted to dark, moist places, such as basements, bathrooms and heavily wooded areas. Mold causes damage and deterioration, and it is also bad for your health. The best way to prevent paper currency from developing mold is to keep it cool, dry and away from dark places that naturally contain mold.
Find a cool, dry place to store your paper currency. Closets, dresser drawers and boxes that will be put into storage are all ideal, as long as they are kept as clean and as dry as possible. A clean area is one that is free of dirt and debris that could eventually harbor mold, or contain enough moisture to attract mold. Keep the air dry by ensuring that any outside drainage is sufficient and by using caulk or a silicone sealant to seal up any cracks around doors, windows and water pipes.
Keep the temperature on the cool side, as cool air doesn't hold as much moisture as warm air does. Run an air conditioner or a dehumidifer as needed. An air condition produces cool air by removing moisture from the environment and then cooling it. Dehumidifers simply remove moisture from the air. Dehumidifers are available in varying sizes; make sure to choose one that is appropriate for the size of the room you wish to dry out. For small storage areas, consider using a product such as Damp Rid (see Resources), which uses special moisture-attracting pellets to remove water from the air.
Store paper currency in special plastic envelopes known as Mylar holders. Unlike normal plastic bags, storage bags and plastic wrap, Mylar holders do not contain any PVC materials, which over time can deteriorate and release chemicals and gases that can damage paper currency and lead to its deteroriation. Place a single sheet of paper currency inside each Mylar holder, and carefully stack multiple Mylar holders together. Secure with a rubber band or a tie, and place the protected paper currency in a cool, dry place.