What characterizes rigid insulation board?

Rigid insulation board is characterized by its composition and physical properties, which primarily involve being made from materials that offer high thermal resistance in a stable form. The correct understanding is that rigid insulation board is typically made from materials like polystyrene, polyisocyanurate, or fiberglass, which are dense and structured, not coarse wood or cane fiber.

The other options suggest properties that do not apply to rigid insulation board. For instance, soft foam indicates a flexible and less dense material, which does not align with the rigid nature of the insulation board. Flexibility is the opposite of rigidity, as rigid insulation boards are designed to maintain their shape under loads and to provide substantial structural support when installed. Lastly, saying that rigid insulation boards are available only in one thickness is misleading, as these boards come in various thicknesses to meet different application requirements and insulation values.

Understanding these characteristics helps in selecting the right insulation type for specific applications, ensuring optimal energy efficiency and structural integrity in roofing systems.