The Baking Sheet Blues

• A baking sheet is more than a platform for your cookies to rest on while the oven's heat does its work. The sheet pan is an active player, with a dramatic and decisive effect on the outcome of your baking. The variance between sets of pans is even more dramatic given that they're almost all made from the same metal. Aluminum is the universal choice for sheet pans, because it offers a stellar combination of heat conduction, light weight and low cost. The differences derive from the weight, color and design of the pans.

You Can Be Too Thin

• Fitness enthusiasts joke that you can never be too thin or too rich, but thinness isn't a good characteristic in a sheet pan. A heavy-duty commercial-style sheet pan is thick enough to absorb a great deal of heat and transfer it evenly from edge to edge. Thin pans are prone to hotter and cooler areas, because minute differences in the pan's thickness affect its ability to transfer heat. This can lead to underbaked and overbaked cookies on different sections of the same sheet pan, a frustration for any baker. Thin pans are also prone to warping in the oven's heat, which can lead to misshaped cookies.

Don't Be Color Blind

• Although sheet pans are almost all made of aluminum, you'll find them in finishes ranging from charcoal gray to a mirrorlike sheen. This also has a dramatic effect on how much heat they transfer to your cookies. Old-fashioned dark pans heat up quickly and often cause scorched or burned baked goods. Shiny pans have the opposite problem, warming slowly and causing thin, flat, poorly browned cookies. Commercial pans have a plain, dull surface that browns the baked goods without scorching them. If you can't find commercial-style pans in your area, adjust your recipes for the pans you have. Reduce your oven temperature or baking time for dark pans, and increase temperature or time for shiny pans.

Insulated Pans

• Many manufacturers take another approach to sheet pan construction, building pans that separate two layers of aluminum with an insulating cushion of air. This slows the transfer of heat through the pan to the bottom of your cookies, theoretically providing more even heating. In practice, the sheets vary widely in quality and in their results, often producing cookies that remain underbaked on the bottom. Before you opt for an insulated pan, look online for reviews and comparison tests of the major brands.