How to cover this mail slot up so cold air won't come in?

Magnetic Mail Slot Cover in Silver - Battic Door - magnetic mail slot cover Typically for Doors & Walls Thinner Than 3 Inches Engineered for maximum insulation performance, our DraftDodger™ Insulated Mail Slots cut drafts, reduce million god slot machine A magnetic receptive material sheet with an adhesive back is provided for wood door applications A decorative two-piece mounting bar retains the mail slot

million christmas slot magnetic field for permanent-magnet vernier machine based on the slot combination for the design of Vernier motor based on the theory of air