Which two forms of insulation can also act as air barriers?

Dense packed cellulose and spray foam (SPF) are both effective forms of insulation that can also function as air barriers.

Dense packed cellulose insulation is installed in a way that minimizes the gaps and voids, which helps to limit air movement. When densely packed into cavities, it restricts airflow, thereby acting as an air barrier while providing thermal resistance.

Spray foam insulation is particularly notable for its ability to expand and conform to surfaces, filling gaps and cracks thoroughly. This creates a tight seal that effectively blocks air from passing through, making it an excellent air barrier in addition to its insulating properties.

Other options do not inherently provide such air barrier capabilities as their structural characteristics or installation methods do not promote the same level of air sealing. This distinction underlines why the combination of dense packed cellulose and spray foam is the correct choice for insulation that also performs as an air barrier.