These coasters are made with origianl Art Resin. It is meant for art on display and thought it is fairly hard, it can scratch if treated improperly. Art Resin is heat tolerant to 120F or 50C according to their website and most people don't have hot mugs much hotter than this. I have personally tested some of my coasters up to 180F without an issues, but to be safe, please stay within their recommended temperatures. These coasters should be dusted (if needed) with a soft cloth and then cleaned with a gentle cleaner and cloth to remove any finger prints, so basically treat it just like you would treat glass.