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Blown-in insulation

Blown-in insulation is loose insulation material (cellulose, glass or stone wool) blown into a cavity until it fills it to a specified density.

Also known as loose-fill insulation, blown insulation, cellulose insulation, dense-pack insulation, insulation

Instead of cutting batts to fit, loose fibres are blown in through a hose until the cavity is full. The material flows around studs, cables and pipes, leaving fewer gaps than cut insulation, which improves thermal and acoustic performance.

The key variable is density. Too little and the insulation settles over time, leaving a void at the top of the cavity; too much wastes material and can bulge the boards. It is therefore installed to a set volume and density per cavity.

Related terms
Building envelopeThe building envelope is the physical barrier between inside and outside: the external walls, roof, lowest floor, windows and doors. Thermal bridgeA thermal bridge is a local area of the building envelope where heat escapes more easily than through the surrounding construction. Wall panelA wall panel is a prefabricated section of wall: a timber or steel frame, often already fitted with sheathing, insulation, windows and services. It is built in a factory and assembled on site.
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