A baking sheet is a heavy, flat steel pan for baking biscuits, rolls, pastries, and similar foods in the oven — also called a baking tray in some regions. Its job is to conduct heat evenly to the bottoms of baked goods while providing a stable, flat surface; heavier gauges resist warping at high temperatures, which keeps cookies uniform. Rimmed versions, often called half-sheet pans, contain rolling doughs and roasting juices, while rimless sheets suit cookies that slide off easily. Dark finishes brown bottoms more aggressively, insulated double-layer sheets protect delicate items, and lining with parchment prevents sticking. A well-seasoned, heavy baking sheet is among the most used tools in any bakery, its performance improving with the patina of years of service.