The design of Tegel Airport is based on a triangular grid and is echoed in the elevation: the ordering principle for both structure and technical installations is the geometry of the triangle. The concrete shell is left exposed both inside and outside. The structural "skeleton" of the building remains legible. Just on the outer facades of the airport terminal, it is used the color red as constitutes the only strong contrast with the gray concrete and the bronze hues of the window glazing and smooth facade surfaces. Furthermore, the double-storey main concourse hall is covered by a glazed roof. The roughness of the concrete receives an appropriate scale and proportion by virtue of staggered surfaces and the plasticity of form. In the interior, it combines with fired floor tiles and a warm color scheme to soften its effect.