A:Answer Hello - Do not use aluminum foil to line oven bottoms. The foil will trap heat below, and upset the performance of the oven. Same is true for similar items such as silicone oven liners. Foil can melt and permanently damage the oven bottom. Damage from improper use of aluminum foil is not covered by the product warranty. Foil may be used to catch spills by placing a sheet on a lower rack, several inches below the food. Do not use more foil than necessary, and never entirely cover an oven rack with aluminum foil. Keep foil at least 1 ½” from oven walls to prevent poor heat circulation. Please let us know if you have any other questions. Best wishes! -Don@GEA