09/11/2025
Blown in Cellulose vs Blown in Fiberglass
Blown-in cellulose has better insulating properties than blown-in fiberglass, with a higher R-value per inch and superior air-sealing capabilities.
R-value and thermal performance
R-value per inch: Cellulose offers a higher R-value (a measure of heat resistance) at R-3.2 to R-3.8 per inch, compared to fiberglass, which typically has an R-value of R-2.2 to R-2.7 per inch.
Cold climate performance: Unlike fiberglass, cellulose does not lose R-value in sub-zero temperatures. In extreme cold, fiberglass can lose as much as 50% of its listed R-value due to air currents, while cellulose's denser composition prevents this effect.
Air sealing: Cellulose, with its dense and heavy composition, fills and seals cavities and crevices more effectively than fiberglass. This greatly reduces air leakage, which is a major source of heat loss.
Blown-In Attic Insulation: Cellulose vs. Fiberglass
Blown-in Cellulose Homeowner Benefits * Higher R-Value per inch. Cellulose has an R-value of 3.5 – 3.7 per inch, where fiberglass has around 2.1-2.7 R per inch.
Moisture absorption: While cellulose can absorb more water than fiberglass, it also manages moisture better. It absorbs and redistributes moisture, allowing a wall cavity to dry in a more controlled manner. Fiberglass does not absorb water but can lose its insulating properties if it gets wet and compresses.
In-use performance: Despite fiberglass's natural fire resistance, high-quality, treated cellulose has been shown in some tests to have better resistance to the spread of fire. This is because its dense packing restricts oxygen flow, preventing flames from spreading. Both materials can achieve the highest Class A fire rating.
Environmental impact
Eco-friendliness: Cellulose is often considered the more environmentally friendly option, as it is made primarily from recycled paper. While fiberglass also uses recycled glass, its manufacturing process is more energy-intensive.
