Durable polyester material over a polyurethane foam pad for a flexible but firm fit with weather-resistant polyurethane coating Friction fit for a secure seal Prevents drafts and heat loss for improved comfort and energy savings The friction fit design ensures that the heat plug is kept secure and in position. Please check your duct size before purchasing. 3 Year Limited Warranty The Heat Plug Cover is a great solution for protecting your home during the cold winter months. Made with durable polyester material over a polyurethane foam pad for a flexible but firm fit, the heat plug prevents drafty air from entering your home and warm air from escaping through the air ducts.