Kristina Karlsson1, Roland Kádár1, Mats Stading1,2 and Mikael Rigdahl1 1Department of Materials and Manufacturing Technology, Chalmers University of Technology, SE-412 96, Gothenburg, Sweden 2SP Food and Bioscience, Box 5401, SE-402 29 Gothenburg, Sweden Foamed polymeric materials have many advantages such as being lightweight, strong with regard to its low weigh, versatile and relatively inexpensive. The majority of the foams are however produced from fossil-based resources. The two major drawbacks of such foams are their non-renewable nature and the difficult recycling process. Research on processing parameters of renewable candidates therefore comes of importance. Cellulose derivatives can be a promising material for foaming applications. They are in a sense lightweight, abundant, renewable and susceptible for modifications in order to be tailored for certain applications. Here, the processing parameters for laboratory-scale extrusion foaming of hydroxypropyl methylcellulose (HPMC) was investigated. Added water was here used as the blowing agent. Previous experiments were used to select suitable grades of HPMC for foaming, in terms of molecular weight, methoxy content and hydroxypropyl content. Initially, a capillary viscometer served the purpose of a batch extruder to study the selected aqueous HPMC-compounds. The foaming ability at different processing conditions was evaluated by this technique and assisted in the establishment of a general processing window in terms of flow rate, temperature and moisture content. The established processing window later served as a basis for the continuous extrusion foaming. The foaming ability was evaluated at different extrusion conditions and the produced HPMC-foams were characterized with regard to their apparent density and by scanning electron/optical microscopy. Key words: cellulose derivatives, extrusion, processing window