air sealing Vs. insulation

In most cases, air sealing and insulation demand specific materials and should be installed separately (air sealing first).

With some exceptions, the general rule is that air sealing doesn’t replace insulation nor insulation dispense with air sealing.

Air sealing vs. Insulation

Air sealing concerns air leaks and their sources: penetrations, openings, cracks. Insulation involves thermal protection of large surfaces. The scope of home air sealing and insulation is, in these cases, clearly different. And the materials used in these functions are also different.

However, since air leakage may also involve the home's shell - the floors, the ceilings, the walls -, in this case, insulation and air sealing may overlap, though only partially. The materials used in this last case are mostly different (house-wraps and sheet goods, that is, air barriers, in the case of air sealing).

Materials

Air sealing products include caulks (for smaller holes and cracks), sealant foams, weather-stripping materials (namely for window and door movable parts) and air barriers for large surfaces and to provide a whole air leakage protection to the house shell.

Insulation materials involve common fiberglass and mineral wool, cellulose and a large set of plastic foams and special materials like ICF or SIPs.

Materials that can provide both insulation and air sealing

Foams are used to seal medium and relatively large openings and penetrations. But in these case, foams are sealing products, not insulation ones.

Rigid Foam: Insulation and Air Sealing However, in some cases, where structural strength is provided by other means, some rigid foams (polyurethane...) can provide both sealing and insulation.

Materials like EIFS or structural sheathing can also provide both air sealing and insulation.

Most insulation materials do not provide air sealing

Common insulation materials (fiberglass, but also mineral wool or cellulose…) don’t stop air leakage (and vice-versa: sealing materials do not provide insulation).

If the insulation materials in your attic or walls are dirty, that is a very telltale sign of air leakage. In this case, the fiberglass or whatever the insulation material you have, it acting like a filter, collecting dirt without blocking significantly the air movement.

In places like walls or the attic, insulation can hide air leaks, making their identification and sealing more difficult.