Loose fill, also known as “blown” or “blown-in,” is insulation applied by pneumatic equipment through a hose and into attics, walls and ceilings. Loose fill insulation is sold in bales that are fed into the machine, which uses air pressure to fluff clumps out of the  insulation and blow it outward to form a blanket.

 

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Several materials are used to make loose fill insulation. Blown fiber glass was introduced during the 1970s; rock wool and cellulose insulation are loose fill products that have been spun into insulation after being reclaimed from other materials, such as rock, slag and recycled paper.

Loose fill insulation has a tendency to settle over time, which reduces effectiveness somewhat. Do-it-yourselfers can successfully add cellulose or fiber glass loose fill to improve attic insulation. Insulating closed walls, ceilings or cathedral ceilings, or the use of rock wool loose fill, is best left to professional installers properly trained in both safe installation practices and preventing insulation gaps.