Like a thin polar fleece type material.
I've fixed the ones I have a couple of times now. For the most part it's a board, some polystyrene balls, piece of cloth that is stapled to the underside of the board and an edging around to make it nice.
When the balls come out I just stuff them again. When the edging comes off I usethese plastic paper binder stuff which i just cut to size as they just cover the staples and makes it look kinda nice.





