He has cooperated with Piet Hein, Grete Jalk, Arne Jacobsen and Erik Herløw and his designs have been produced by Iform, Fritz Hansen and Dansk. Karpf worked with the idea of the Voxia collection for over twenty years before his ecological furniture achievement was finally realised. His patience was quickly rewarded with numerous awards* and a place in the permanent collection at the Museum of Modern Art in New York. Karpf experimented with flexible, simple seating solutions incorporating stacking and folding when developing his NXT, Oto and Tri plywood chairs. The first prototype for NXT was developed in 1962 although the design was not patented until 1986. *Design Awards for VOXIA collection:1993 Forsnäs Prize2000 IF Ecology Design Award2000 IF Design Award2001 IF Design Award2001 Red Dot