[en] Since three years we have been designing, constructing, and operating hydrogen bubble chambers as vertex detectors for charm physics in hadron beams. The principal design considerations must take into account the formation of small bubbles of correspondingly high density along the tracks. This asks for expansion cycles which are close to the foam limit of hydrogen. To achieve this goal, we need a clean bubble chamber without any seals, which could favour parasitic boiling. To realize such a clean hydrogen chamber, we decided to construct its body entirely from plastic material. For photography this material must be transparent to visible light. (orig./HSI)