| abstract |
A composite board or panel has a lightweight central layer of for example cellulosic material such as paper "honeycomb". In each face of this there is adhered a facing layer of paper or paperboard. Each face of each facing layer is coated with an inert material impervious to water or water-vapour such as polymers, bitumen or waxes. Outermost paper or foil layers can be provided on each face of the composite. The composite is particularly resistant to uptake of water and thus does not warp. |