Maize flour and blends from starch and zein biopolymers were processed as dense materials by extrusion (120 degrees C, 300 J.g(-1)) and press-molding (140 degrees C, 10 min) at a constant moisture content (26% wb), and then foamed by microwave heating. The mechanical properties of foams, determined by a 3-point bending test, were governed by density, in agreement with an open solid foam model. The density and 3D cellular structure of the foams were determined by X-ray tomography. In the same interval of density [0.15, 03 g.cm(-3)], foams from microwaved materials had a finer cellular structure than directly expanded materials at extruder outlet. The study of melt rheological behavior with Rheoplast (R) (100-160 degrees C, SME <= 200 J.g(-1)) showed that protein content (0-15%) did not affect shear viscosity but increased elongational viscosity. This trend, similar to the one reported for the storage modulus in a rubbery state, could be attributed to dissipative effects in a starch/protein interphase, explaining the difference of expansion between starch, blends and flour.