Fibreglass insulation is the most widely used thermal insulation material in North American residential construction, installed in approximately 70% of new single-family homes. The material consists of extremely fine glass fibres, typically 3 to 20 microns in diameter, bonded into a wool-like matrix that traps air and resists heat transfer. Fibreglass insulation was first commercially produced by Owens-Illinois in 1938 and has dominated the market continuously since the post-war building boom of the 1950s.
How Fibreglass Insulation Works
Thermal energy moves through building assemblies by three mechanisms: conduction, convection, and radiation. Fibreglass insulation primarily resists conduction by trapping air within a matrix of fine fibres. Air itself has very low thermal conductivity, approximately 0.026 W/m.K, but only when it is prevented from moving. The glass fibres create millions of small air pockets, each too small for convective currents to develop, effectively immobilising the air and reducing heat transfer. This is why compressing fibreglass insulation reduces its R-value: the compression eliminates the air pockets that provide the insulating effect.
R-Value Ratings and Performance
The R-value measures thermal resistance in units of ft2.F.h/Btu (imperial) or m2.K/W (metric). Fibreglass batts deliver R-2.2 to R-2.7 per inch of thickness depending on density and manufacturing process. High-density batts, such as Owens Corning's PRO Pink line, achieve R-3.0 per inch or slightly higher. Typical batt thicknesses and their corresponding R-values for standard-density fibreglass are:
- R-11: 3.5 inches (fits 2x4 stud cavity)
- R-13: 3.625 inches (fits modern 2x4 stud cavity at actual 3.5" plus slight overfill)
- R-19: 6.25 inches (fits 2x6 stud cavity)
- R-30: 9.5 inches (fits 2x10 joist cavity)
- R-38: 12 inches (fits 2x12 joist cavity or can be split)
These rated R-values assume proper installation with no compression, gaps, or voids. Real-world performance, often called effective R-value, can be substantially lower due to installation defects. A California Energy Commission study found that typical residential fibreglass batt installations lose 20% to 30% of their rated R-value due to compression around electrical boxes, gaps at edges, and incomplete filling of stud cavities.
Blown-in loose-fill fibreglass achieves R-2.2 to R-2.7 per inch when installed to the manufacturer's specified density. The advantage of blown-in is that it fills irregular cavities completely, eliminating the gaps and voids common with batt installation. Blown fibreglass is typically installed using a pneumatic blowing machine that fluffs the material and propels it through a hose to the installation point. Coverage is specified by weight per square foot and installed thickness.
Product Forms: Batts, Rolls and Blown-In
Batts are pre-cut rectangular pieces, typically 47 to 93 inches long and sized to fit standard stud and joist spacing of 16 or 24 inches on centre. Rolls are continuous lengths of uncompressed insulation, usually 40 to 60 feet long, cut to length on site by the installer. Rolls are more economical for large, uninterrupted areas such as attic floors but require more labour to cut and fit precisely.
Blown-in fibreglass is the preferred form for attic applications because it can be installed to any depth, achieving R-values of R-38 to R-60 or higher in a single continuous layer. It is also used for filling enclosed cavities in existing walls through small access holes. Attic coverage is verified by measuring the installed depth: for standard-density blown fibreglass, 15 inches provides approximately R-38.
Formaldehyde-Free Binders
Traditional fibreglass insulation used phenol-formaldehyde resin as the binder that holds the glass fibres in a cohesive mat. During manufacturing and for a period after installation, these binders off-gassed formaldehyde, contributing to indoor air quality concerns. In 2002, Johns Manville became the first major manufacturer to convert to a formaldehyde-free acrylic-based binder. Owens Corning followed with its EcoTouch and later PINK Next Gen Fibreglas products, both using plant-based or acrylic binders with no added formaldehyde. As of 2024, essentially all fibreglass insulation sold in North America for residential use is manufactured with formaldehyde-free binders. Products certified under GREENGUARD Gold meet stringent VOC emission limits for use in schools and healthcare facilities.
Recycled Content and Manufacturing
Modern fibreglass insulation incorporates 40% to 60% post-consumer recycled glass content by weight, primarily from container glass collected through municipal recycling programmes. Owens Corning reports an average of approximately 53% recycled content across its North American residential insulation products. The use of recycled glass reduces the energy required for manufacturing by approximately 10% to 15% compared to using virgin raw materials, as the recycled glass melts at a slightly lower temperature. The manufacturing process itself involves melting the glass batch in a furnace at approximately 1,400 degrees Celsius, then spinning the molten glass through tiny holes in a rapidly rotating spinner to form fibres. The fibres are sprayed with the binder, collected on a conveyor, and passed through a curing oven where the binder sets.
Owens Corning and Market Position
Owens Corning, headquartered in Toledo, Ohio, is the largest fibreglass insulation manufacturer in North America. The company's distinctive pink colour originated in 1956 as a marketing decision; the pink dye has no functional purpose beyond brand identification. Owens Corning holds the registered trademark for the colour pink as applied to fibreglass insulation, one of the few colour trademarks in the building materials industry. Johns Manville (a Berkshire Hathaway subsidiary), CertainTeed (a Saint-Gobain subsidiary), and Knauf Insulation are the other major producers in the North American market.