Loose fill insulation is any form of thermal wall insulation consisting of discrete particles, fibers, chips, dust, or other pieces, which are packed, stuffed, taped, or otherwise inserted into the walls. This can include fiberglass, straw, wood chips, cotton, loose synthetic materials, or any other wholly loose or loosely bound objects used for this purpose. This does not include forms of batt insulation, which are loose materials held together by a bag, sheet, quilt, or other integrated covering.

The insulating material enters the wall as separate particles, fibers, or other pieces. Its substance can be natural or synthetic without changing that loose physical form.

Batt insulation holds the material together as a mat, pad, or integrated covered unit. A panel instead retains a rigid sheet form.