Terlulu Stainless Steel Baking Tray Set USEING INSTRUCTION Please Preheat the oven tray evenly before use can prevent warping. Please rest assured if it does, it is SAFE and will RUTERN to its original shape when it cools.Please put some oil on it or use parchment paper to avoid food sticking. WARM TIPS: How To Maintain: The trays can be cleaned in the dishwasher, but thanks to their non-stick properties, it is recommended to clean these trays in the sink as hand washing is kinder to metal dishes.Please use soft cleaning rag to clean the baking sheets for the beauty of its surface.Please clean and dry thoroughly before storing for its durability.