Wood foams are light wood-based materials (40 - 280 kg/m³) with an open-pore texture made up of finely ground wood. They take their strength from the wood’s own binding characteristics and therefore do not need any synthetic adhesives. This means that the foams consist completely of renewable material.
At the Fraunhofer WKI, the latest methods are being developed by means of which pressure-resistant foams from lignocellulose can be produced specifically with regard to their pore structure. For the starting material, both deciduous and coniferous wood are suitable. As the wood is finely ground, wood from forest thinning as well as sawmill by-products can also be used as raw materials; even the use of non-wood-containing lignocelluloses, such as hemp or straw, is possible.
The foam products have already been tested according to the relevant insulation standards. Promising results were achieved both in terms of their heat-insulation and physical properties. The compression strengths at 10% pressure range from 20 kPa to 190 kPa depending on the density. Heat conduction is also density-dependent and is below 0.04 W/mK for low densities. This is comparable to the values for polystyrene and wood-fiber insulation boards. Swelling after 24 hours in water is below 1% and the foams retain their shape. Fire behavior is similar to that of natural fiber insulation materials. They burn and smolder and the flames go out partly by themselves. Additives which may be necessary for fire safety can simply and efficiently be added during the manufacturing process by mixing them with the fiber materials.
The foam takes its strength from the wood’s own binding characteristics and therefore does not need any synthetic adhesives. This means that there can be no health issues caused by emissions from adhesives.
In the evaluation of products according to their climate-damaging CO2 equivalents or their carbon footprints, foamed wood is extremely attractive as a particularly sustainable and completely natural material. The material has a high market potential, as it provides - particularly for private housing construction - a promising alternative to synthetic polymeric foams. The Fraunhofer WKI is working intensively on the further development of wood foams in order to enable this unique natural material to be industrially-produced and available on the open market in the foreseeable future.