This sponge is tough. I watched a video on YouTube of how to use it on an oven. The woman was pushing really hard. I didn't push as hard, yet was persistent on my ovens glass door and inside. When I was cleaning, I couldn't see any scratching. When the glass is wet and using the sponge, it's very easy to miss damage being done with this mighty little sponge. All I noticed was the gunk finally coming off. It took a heap of effort. I was at that door for a very long time. I was surprised how long it took me. However, when it was done (I stopped eventually as I was tired), most of the film that'd been on the door was gone! However, i had also scratched the surface a great deal - that was only visible when dry. When Koh suggest a test patch first - please do this. Choose a small corner, maybe 50 cent size or so and do that first. If you start and it's coming off easily, still stop and wait until the glass is completely dry, so you can check if there's scratches. By completely dry, I mean completely dry. Spray the Koh on test patch area, clean with the sponge, wipe clean, leave for a few minutes, then check it before continuing. Use the smallest amount of pressure required with this sponge as possible. It's a mighty sponge that will do the work for you. It's quite amazing. The YouTube bloggers are misleading in how they use these sponges. Be as gentle as possible, you can always add pressure, yet once damage is done, it's done. It's easy to become carried away by seeing the glass coming clean, and forget it could be being scratched in the process by too much enthusiasm 🙂 Please stop intermittently to double check the pressure isn't too hard, and the glass isn't being scratched. Also, as Koh warned, the sponges do catch on the rack ends, and this does damage them. Took little chunks out of 2 of mine, sadly. Thought I was being really careful. Didn't realise until afterwards. Koh do warn people. I hope this review helps someone. They're easy to clean. Spray with Koh and rinse. It really is that easy. I highly recommend these items, if a person is very gentle, does the test patch first (as Koh recommend), and stops to check regularly that no damage is being done. As I've said, it's easy to become carried away with the happiness of seeing the oven clean, and not realise what's going on, as it's wet and hard to see it being scratched. Please be careful. This mighty little sponge is powerful!