This professional-weight muffin pan was developed for us by Chicago Metallic. The aluminum-coated steel is heavier in gauge than that of standard home bakeware and won't rust or warp. Extremely durable, the aluminized steel heats quickly and evenly to ensure uniform baking. With use, the metal darkens slightly, increasing its ability to absorb heat. The pan is finished with rolled rims. The 24-cup mini-muffin pan is 15 3/4" x 11".