Method and apparatus for producing solid foam, product and use

A method for producing a solid foam continuously, in which a homogenous suspension is formed from a raw material, air is added to the homogenous suspension to form a foam mixture, and the solid foam is formed from the foam mixture, wherein the method comprises:

• forming the homogeneous suspension from a bio-based raw material comprising fibers in which the homogenous suspension comprises a solidifying agent;
• adding a chemical which lowers surface tension and increases viscosity to the homogenous suspension and which is selected from methylcellulose, derivate of the methylcellulose, carboxymethyl cellulose, hydroxypropyl cellulose, ethyl cellulose, or one of their combinations;
• forming the foam mixture which comprises bubbles by mixing air bubbles into the homogenous suspension;
• and
• treating the foam mixture by an extruder and injecting the foam mixture from the extruder to a moving surface via at least one nozzle to form a foam pattern which comprises parallel foam stripes to create a rod-shaped structure and laying the foam pattern on the moving surface and solidifying the foam mixture of the foam pattern using heat in order to form the solid foam having anisotropic properties and comprising bubbles such that the bubbles of the foam mixture shrink in off-length directions to form elongated bubbles in the solid foam.