Clothes, particularly those made from natural fibers, need air circulation, says Stu Bloom, the owner of Rave FabriCare, a garment- and textile-care company in Scottsdale, Arizona. Airtight containers can hold moisture in fabrics, potentially causing mold, mildew, yellowing, or a musty odor. Already own plastic bins? Poke a few holes in them, or cover stacks of sweaters with old, clean cotton pillowcases or sheets to protect them from dust when they're stored on a shelf. Pack the heaviest items on the bottom, the lightest on top.