Wood composites had a theoretical superiority as the structural material for airships up to a certain size, after which the superior strength of aluminum (and later duralumin) in tension was more important than the superior strength of wood in compression. Schütte-Lanz airships until 1918 were made of wood and plywood glued together. Moisture tended to degrade the integrity of the glued joints. Schütte-Lanz airships became structurally unsound when water entered the airship's imperfectly waterproofed envelope. This tended to happen during wet weather, but also, more insidiously, in defective or damaged hangars. In the words of "Führer der Luftschiffe" Peter Strasser: