What type of insulation is recommended for use with a vapor barrier on the warm side?

Fiberglass insulation is recommended for use with a vapor barrier on the warm side because of its moisture resistance and low cost. When installed correctly, fiberglass does not absorb moisture, which helps maintain the integrity of the vapor barrier. The vapor barrier prevents warm, moist air from reaching the cooler surfaces of the exterior wall, where condensation can occur. This is crucial in areas with significant temperature differential between the inside and outside environments.

Fiberglass insulation traps air within its fibers, providing thermal resistance, while still allowing any vapor that may occasionally escape through the insulation to pass through without causing damage to the materials surrounding it. It also adheres to building codes that call for the appropriate installation of vapor barriers in climate conditions where moisture accumulation can be a concern.

Other types of insulation, such as spray foam, cellulose, and mineral wool, have different moisture management characteristics. Spray foam can create an airtight seal which may or may not be appropriate depending on the climate, as it can trap moisture rather than allowing it to escape. Cellulose insulation can absorb moisture and may require careful management to ensure moisture does not lead to mold growth. Mineral wool is also resistant to moisture but does not perform as well in terms of insulation efficiency with vapor barriers as fiberglass does.