What type of insulation is least likely to absorb moisture?

Fiberglass insulation is the type that is least likely to absorb moisture. This characteristic is primarily due to its composition; fiberglass is made from glass fibers, which do not absorb water. As a result, fiberglass insulation maintains its thermal and structural integrity even in humid conditions, preventing issues such as mold growth or the degradation of insulating properties that can arise with moisture-absorbing materials.

In contrast, cellulose insulation, which is made from recycled paper products, can absorb moisture quite easily, leading to potential problems if not properly managed. Mineral wool insulation, while resistant to fire and also water, can still retain some moisture, especially if exposed to extended periods of wetness. Spray foam insulation generally does not absorb moisture, as it creates an airtight seal that helps in reducing humidity levels; however, it may not be as effective in high-moisture environments as fiberglass. Therefore, in terms of moisture absorption specifically, fiberglass stands out as the most resistant material.