The powers of carbon and fine-mesh netting combine in the 8-inch DuraBreeze® Duct Defender to protect duct systems against bugs, mold, mildew and unpleasant odors. Use the simple Velcro tabs to attach it to the fan intake to prevent pests from entering, or affix it to the fan exhaust to keep unpleasant odors from escaping. Replacement carbon filter inserts are available separately.