I purchased this set of cookie sheets, and the first time I used them, I hear a loud popping noise. I ran over to the oven, only to discover that the sheet bends up at the corner when hot. They flatten back out after cooling off, but it is a little irritating to hear horrible noises from the oven whenever I use them, and the bending causes things on the sheet to move around. These cookie sheets are good as far as nonstick aspect, but I would never purchase them again and do not recommend them for anyone that cares about what they are baking.