It is made of plastic.
I have had two seat covers of the same model for almost 4 years. The no slam part on one of them suddenly stopped working. So the old one would just slam instead of slowly closing. We replaced it with this new one and hope it will last longer.
Thank you for your recent inquiry with The Home Depot. I do not know that we would carry a specific hinge type to fit your American Standard Champion 4 Slow-Close Elongated Closed Front Toilet Seat in White (307823394). One idea I do have is it may be possible to find a small hinge that may meet your needs at your favorite Home Depot Store. We appreciate your business and look forward to serving you in the future.