Can I use aluminum foil or parchment paper inside the oven?

You should never cover the crumb tray or oven walls with aluminum foil or parchment paper, as this can cause overheating or fire. You may use foil or parchment paper as a liner on the baking pan only, but it must be cut to the exact size of the pan and must never be left in the oven during preheating or cooking unless food is on top of it to weigh it down.