Wendy Mills, age 12, of Watertown, N.Y., for her question:

HOW IS MINERAL WOOL MADE?

Mineral wool is used for packing around heated objects, such as steam pipes and boilers, to prevent the escape of heat. It is also used to protect water pipes from frost and as matting under floors to deaden sound.

Mineral wool is an insulating material made from the minerals which are taken from iron making blast furnaces as refuse, or slag.

To make mineral wool, the molten slag is forced by steam pressure through a crescent shaped opening. It cools in long fibers which are pressed into mats. Mineral wool is sometimes called mineral cotton or slag wool in industry.  More popular than mineral wool as an insulating material is asbestos.