1. Opt for heavy-gauge aluminum with low sides or no sides at all.
2. Invest in lighter-colored cookie sheets. If sheets are too dark, cookies may overbrown.
3. Select sheets with a dull finish so cookie bottoms brown more evenly.
4. Use shiny sheets for cookies that should not brown on bottoms, such as shortbread.
5. Use nonstick cookie sheets if you prefer to skip the greasing step. However, the dough may not spread as much, resulting in thicker cookies with smooth bottoms.
6. Use insulated cookie sheets selectively. They are fine if you want pale drop cookies with soft-set centers. You may have trouble using them for cookies high in butter, shaped cookies, and some drop cookies because the butter may start to melt, leaking out before dough is set. And because dough spreads before it sets, cookies may have thin edges.