Tego film is an adhesive sheet, used in the manufacture of waterproof plywood. It is applied dry and cured by heat, which allows for high-quality laminates that are free from internal voids and warping. Tego film plywoods were used in aircraft manufacture in Germany during World War II, and the loss of the plant during a 1943 bombing raid was a serious blow to several aircraft projects.
Tego film was developed in Germany around 1930 as a glue for waterproof plywood. It comprised a paper sheet pre-impregnated with a resole phenolic resin. When heated, assembled between wood veneers and then compressed, a strong and waterproof laminated plywood was formed. Most plywood at this time used other adhesives, such as casein. These adhesives were generally applied as aqueous solutions, which caused warping of thin veneers and made it difficult to achieve a solid laminate without risk of voids. As Tego film was used dry, it gave a high integrity result, solid and without risk of hidden weaknesses. This became an important factor in time, when it was applied to use in aircraft construction.
This adhesive was unique at its time and was only available as the Goldschmidt product line from its makers Goldmand AG of Wuppertal. By 1932 it was being exported worldwide.
The de Havilland Albatross airliner of 1936 had a fuselage of wooden sandwich construction: wafers of birch plywood were spaced apart by a balsa sheet and glued by a casein adhesive. This same construction, but with Aerolite, a urea-formaldehyde adhesive, achieved fame with its wartime use in the DH.98 Mosquito fast bomber. As well as being a construction of light weight and high performance, it also avoided the use of aluminium, a strategic material during wartime, and could use the skills of woodworkers, rather than those of specialised aircraft metalworkers.