Abstract: A panel comprising fillers embedded in a closed cell expanded phenolic resin is made by making a mixture, which is initially fluid, or phenolic resin, a hardening agent, a surface active agent and a porogenic agent, which has a boiling point above ambient temperature and below the polycondensation temperature of the mixture. This liquid mixture is mixed with fillers, for example balls or microspheres of glass or expanded material such as polystyrene. The resulting mixture is placed in a mould, only partially filling the mould, and heated progressively to a temperature in the neighborhood of the boiling point of the porogene agent, while evacuating the mould, and held at that temperature until the mixture has expanded to fill the mould. The temperature is then progressively increased to the polycondensation temperature to harden the expanded mixture.

Abstract: A panel comprising fillers embedded in a closed cell expanded phenolic resin is made by making a mixture, which is initially fluid, of phenolic resin, a hardening agent, a surface active agent, a finely divided hydrophilic material and a porogenic agent, which has a boiling point above ambient temperature and below the polycondensation temperature of the mixture. This liquid mixture is mixed with fillers, for example balls or microspheres of glass or expanded material such as polystyrene. The resulting mixture is placed in a mould, only partially filling the mould, and heated progressively to a temperature in the neighborhood of the boiling point of the porogene agent, while evacuating the mould, and held at that temperature until the mixture has expanded to fill the mould. The temperature is then progressively increased to the polycondensation temperature to harden the expanded mixture.