Abstract: A semi-flexible or flexible phenolic foam composition having a substantially open cellular structure. It comprises the reaction product of a mixture of a phenol-aldehyde resin, a surfactant, a blowing agent; optionally a wetting agent and a catalyst. Also within the scope of the present invention is a method for producing a semi-flexible or flexible phenolic foam composition having a substantially opened cellular structure. This method comprises mixing a phenol-aldehyde resin with a surfactant, a blowing agent and optionally a cell opening and wetting agent; curing the mixture by reacting it with an acid catalyst; compressing the cured or semi-cured product below its original thickness and releasing the pressure, thereby obtaining the desired semi-flexible or flexible phenolic foam composition. The semi-flexible or flexible foam thus obtained possesses excellent insulation and flame retardant properties.