Batt insulation refers to mats or pads of thermal insulation materials which can be stuffed into empty spaces or pressed against a wall. Unlike panels they are not rigid, but unlike foam or loose fill they hold together on their own. Batts can be plain meshes of fibers bound to each other, or they can be held together by a sewn or sealed wrapper, often like a bag. This form is very commonly used when insulating many separated spaces in a wall or roof, such as the spaces between wooden struts which run perpendicular to a flat wall surface.

The flexible insulating mass holds together as an individual mat, pad, or wrapped unit. This cohesion distinguishes a batt from material placed as loose fill.

The batt form can contain different fibers. Fiberglass, wood fiber, and cotton describe the material within that form.