The door seal ensures the door on your tumble dryer forms a tight seal when closed. It also acts as a kind of airlock between the drum and main body of the dryer.
Is the door on your tumble dryer no longer forming a tight seal when closed? The seal itself will undoubtedly be the cause.
With repeated use, the seal can eventually become misshapen and end up preventing the door from closing properly.
It's also possible for the door seal to get mouldy or fouled up, in which case first try cleaning it. If that's not sufficient to solve the issue, you'll need to replace the seal.
Find the right door seal to fit your tumble dryer right here. Large number of models available!