What type of insulation should be protected from sunlight?

Rigid board insulation should be protected from sunlight primarily because exposure to ultraviolet (UV) radiation can cause degradation of its materials. Many rigid board insulations, especially those made from expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate, can suffer from a loss of structural integrity and thermal performance when exposed to prolonged sunlight.

In addition, the surface of rigid board insulation may become brittle over time, which can lead to diminished effectiveness as an insulative barrier. Protecting it from UV exposure ensures that the insulation maintains its intended R-value and extends its lifespan in the application.

The other types of insulation mentioned, while they may have their own protective needs, do not typically face the same level of concern regarding UV degradation. Loose fill insulation can be affected by settlement or moisture but is usually not placed in a way that exposes it to sunlight directly. Fiberglass batt insulation is often faced with a vapor barrier or is installed within confined wall cavities, limiting its exposure to sunlight. Foam in place insulation is applied in situ and thus inherently avoids significant UV exposure during its installation process. Therefore, the focus on protecting rigid board insulation from sunlight is specific to its material properties and the structural integrity necessary for effective thermal performance