Curly iron is for naturally straight hair or for naturally curly hair?

huh??? It can be for any hair.

Curly iron is for naturally straight hair or for naturally curly hair?

You can use a curling iron with any type of hair. If your hair is very straight, use a smaller in diameter iron, at least 1 in. spray a section of hair before you curl it and use a hotter setting. If your hair is extremely curly, it may work better to use a ceramic home hair straightener before you use the curling iron. Then use a wider in diameter iron to make soft curls. If your hair is slightly damp the ceramic straightener will work better.