differnt brands are made different ways but basically the edge channels pry off and the fabric is captured in a channel. pull the fabric out and stretch new push into channel. I have seen some that is stapled and some that is glued. but I think most is just stretched like an artist canvas. I have seen re-conditioners take these apart, repaint the frames and re-stretch the fabric. The cores are sometimes fiberglass board, sometimes paper honeycomb and I have seen partical board. Years ago I had a pile I gave to a scrapper to get rid off, and he was nice enough to leave a pile if partical board behind.