Can I use this to coat the back of a piece of indoor/outdoor carpet to be used as a replacement foot mat in a car?

Hey there, thanks for reaching out. Customers are always finding new and inventive ways of using our products beyond their intended design with mixed results. Flex Seal Liquid will adhere to the carpet and work well to keep any liquid from seeping through to the floor. However, we do not recommend Flex Seal Liquid for underfoot applications where the surface may come in contact with liquid as it may become slippery when wet. We recommend testing a small area first to make sure you get the result you are looking for before completing the project especially for applications beyond the design of the product like this. If you have any other questions or need project-specific help, send us an email at humans@flexsealproducts.com or a DM on socials. We're here to help!