The best way to store wool sweaters is in a cotton bag, such as a pillowcase. Larvae will not eat through a cotton barrier to get to a wool sweater. If a cotton bag is not available, then a paper bag also works to protect wool sweaters.
Be sure that the bag's end is folded over and sealed with tape or staples. Other options for storage include cedar chests and plastic bags, though neither allows for air circulation. No matter which storage option you choose, always be sure that the wool sweaters are clean and completely dry prior to placing them in storage.