Convertible baking pans consist of two nesting pieces. Bake with both pieces in place to create an insulating layer of air that guards against over-browning and burning. After baking, flip the bottom piece over to create a lid that locks in place for easy storage and transport. The pans are made of anodized aluminum for rapid and uniform heating; the locking posts are made of stainless-steel for durability. The Convertible cake pan measures 9" x 13", the Convertible brownie pan measures 9" x 9".