Batts are the most common form of fibrous insulation. These are flexible strips of insulation in various thicknesses usually sized for specific spaces such as filling the empty spaces between studs in a wall or between rafters in a roof.
Loose insulation is blown through a tube into an area until the desired volume and density is achieved. One typical location is above the ceiling of a home. Fibers insulation is often blown into the attic where it settles on the ceilings of the rooms below.
Another common installation is in the spaces ("cavities") between the inner and outer surfaces of exterior walls and between the vertical wood structural supports ("studs"). Often, loose fibers of wood ("wood fiber"), glass ("fiberglass"), or recycled post-consumer paper (“cellulose”) are blown into those cavities to a specific density (e.g., 3.5 pounds per cubic foot of cellulose) to prevent the fibers from settling from their own weigh over time creating a void with only air at the top of the cavity.
Fibrous insulation of all kinds can be pressed into rigid panels which are mechanically fastened to walls, floors, and roofs. These panels are typically sized in standard lengths such as 24” wide by 8’ long and 4’ wide by 8’ long. They come in thicknesses from 1/2” to 6” thick.
Another related insulator is cork (from the bark of certain oak trees) which is pressed into rigid panels.