Polyisocyanurate, commonly called polyiso, is a high-performance, rigid foam insulation widely used in construction for its excellent thermal resistance and fire protection. It's often used in roofs and walls, both in commercial and residential applications. https://www.diveboard.com/dohod47278/posts/on-polyisocyanurate-a-modern-solution-for-smarter-insulation-B6zqZJ0