It's a piece of hard acrylic. What you see in this picture is what you get. Takes off anything you care to be stubborn at, though big hunks of coraline can take some work. And, unlike a razor blade, it can't scratch your glass! (Provided you don't get any sand or anything snagged under it, but that should be relatively tricky.)

This was just a fun little add-on to an order but haven't been able to find the utility of it over using a regular razor blade in scraping algae from the inside glass.

Size is perfect for the wallet so I always have a scrubber on me. It also doubles as a cool filter to make corals pop when you look through it.