What characterizes rigid insulation board?

Rigid insulation board is characterized by being composed of materials that provide a high degree of thermal resistance while maintaining structural integrity. Option B correctly identifies that rigid insulation board is made of materials like rigid foam, which can include polystyrene or polyisocyanurate, and sometimes may incorporate elements like coarse wood or cane fiber in certain types of insulation products, contributing to their structural rigidity.

Rigid insulation boards are typically designed to remain solid under pressure, providing effective thermal barriers in various constructions. This distinguishes them from other types of insulation that might be more flexible or less dense, allowing for easier handling and installation in specific applications.

Other options do not accurately represent the characteristics of rigid insulation boards: the first option describes a soft foam which is contrary to the rigidity; the third option suggests flexibility, which misrepresents the structural nature of rigid boards; and the last option implies a limitation in thickness, whereas rigid insulation boards come in various thicknesses to suit different building requirements.