Phenolic boards are manufactured from a plastic foam which forms an insulating core between two flexible facing layers. The phenolic foam has a high closed cell content and fine cell structure, similar to PIR boards. Rigid phenolic insulation is produced by mixing high solids and phenolic resin with a surface-acting agent. The heat created by the reaction makes a mass of tiny bubbles in the material. The phenolic foam is then cured and manufactured continuously to create thin sheet material laminated with various facings and cut into boards.