'Thorax' is a seminal example of Koehler's technique of 'Décollage Positiv-Negativ' in which he carefully tore away a layer of paper by hand to then fold it over and glue it down to permanently show its underbelly. These works bear testimony to Koehler's dedication to the aggressive-destructive moment of creation, tamed by a controlled masterly execution. Along those principles, Koehler forged a remarkable and unique body of work including sand-paintings, works with broken glass and ceramics, and works created with burning forks. Koehler's incomparable artistic achievements bear testimony to his powerful creative mind and individual expression which can be situated central to the German 1950s avant-garde, matching the endeavours of Otto Piene, Heinz Mack, Emil Schumacher and Wolf Vostell.

The work of Koehler is in the following museums: Museum Wiesbaden, Wiesbaden; Wilhelm Hack Museum, Ludwigshafen; Kunsthalle Bielefeld, Bielefeld; Kunstmuseum Bochum, Bochum; Museumlandschaft Hessen, Kassel; Goethe Institut, Munich; Städtische Galerie, Wolfsburg; Museum Moderner Kunst Stiftung Ludwig, Vienna; The European Parliament, House of Europan History, Brussels.