The term "batt" refers to the form the insulation comes in. When you open a package of batt insulation, you will find the insulation divided into several rectangular pads. Batt insulation is made to fit between normal stud walls easily. The sheets are usually 16 or 24 inches wide to fit between studs, and 4 or 8 feet tall to match the height.
Batt insulation comes in several different varieties. The first is fiberglass. Overall, fiberglass is the most common material used in insulation, and it is still the most common form of batt insulation. Mineral wool products, such as rock wool, are also becoming more common and are used frequently. Other batt insulation products are available, such as those made from synthetic or natural fibers, but these are less common.
The primary use of batt insulation is for insulating attics and walls with uniformly spaced studs and joists. This makes it easy to fill the spaces with the batt products. If you have to insulate around corners or in small areas, some batt insulation can be easily torn so that you can get a piece the exact right size to fill in the gaps or nooks and crannies that confront you.
When you install fiberglass batt insulation, aim to have no gaps or spaces that are not filled by either wood or insulation. Tear the insulation or cut it with a utility knife to make it fit around electrical outlets and behind wires. A putty knife helps you stuff thin strips of insulation into any gaps you might have to ensure they are filled. Finally, once all the insulation is in place, staple a plastic vapor barrier on top of the wall before your wall covering is put up.