What pans cannot be used on cooktops?

Certain pans cannot be used on cooktops, including those made from materials that do not conduct heat well, such as glass or ceramic that isn't labeled as cooktop-safe. Additionally, pans with warped or uneven bottoms can result in poor heat distribution. Cookware with non-flat bases, like some woks or pans with raised edges, may also not work effectively on flat cooktops. Always check the manufacturer's guidelines to ensure compatibility.