Strong magnetism – The cover is made of thick strong magnetic material, which can firmly hold the vent in place | Custom Fit-The size (5.5 "X 12") fits most standard air conditioners. In addition, you can easily cut it into any shape to completely seal the air | Increase of Efficiency-By redirecting the air and reducing energy costs, you can efficiently distribute airflow or conveniently close registers in unused space. Save your energy, save your money and make your home more comfortable | Multipurpose&multi-function-Our magnetic ventilation covers are versatile and versatile, ideal for indoor or outdoor HVAC and RV use | Purchase Tip: Our magnetic ventilation cover can only be used for ventilation covers with iron surfaces. If the surface is made of steel, aluminum, or wood, it cannot be used. Please purchase with caution!