My Kitchen Cook & Bake Baking Sheet 5 "Super non stick but warps in oven" Janet 01 April 2014 The first time i used this tray i was making Pitta bread and the tray had to be in a hot oven (gas 8) for 15 minutes before putting the dough on it. When i took it out of the oven to use it was all warped. It did return to shape when cold but it is advertised as non warping. I decided to try it again and it remained straight. Have used it now every week for over 6 months with absolutely no problems. It must just be the first time it is used that it warps.