In recent years, there has been some debate over which insulation products are better at reducing air infiltration. The fact is reducing air infiltration in a home is largely dependent on the air sealing package, not the insulation installed in the wall cavity. A new report published this fall from Building Science Corporation (BSC) affirms that insulation, of any type, is no substitute for proper air sealing and prevention of air infiltration. BSC’s multi-year insulation research project entailed a baseline set of seven test walls, including fiber glass batts, cellulose, spray foam and extruded polystyrene.

The study produced several significant findings:

On Air Infiltration

When walls are constructed with the same installed R-value in the stud space, and are air sealed both inside and out (with effectively zero air leakage through the assembly), they exhibit essentially the same thermal performance regardless of the type of insulation used.

On Convection

All of the reference test wall assemblies were subjected to significant temperature differences. Natural convective loop heat loss, or heat loss that occurs when heat is conducted from the building interior into an enclosed space within the thermal envelope and then transferred convectively through the thermal envelope, was not observed in any of the wall assemblies.

On Thermal Bridging

Every insulated wall assembly experienced a small loss in thermal performance due to air movement through the assembly. Additionally, thermal bridging through the framing resulted in a roughly 15 percent decrease in thermal performance regardless of the type of insulation material used in the stud space.

For most builders, fiber glass insulation is the preferred insulation system for several reasons. It offers unmatched value versatility, good thermal performance and functions equally to other insulation systems when used with an air sealing package. Fiber glass batts are generally lower in cost to install and contain recycled glass (up to 70 percent post-consumer product). Finally, fiber glass insulation is the most thoroughly tested insulation product on the market.

Even as building technologies expand and become more efficient than ever, fiber glass insulation remains the leader in home insulation because of these high-performance attributes.

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