[en] We describe both a method to produce a low density foam and a small mechanical apparatus used to embed a microsphere in the foam. Freeze-drying techniques offer an efficient way to create low density foams. Good results are obtained with 3%--5% of dextran in water. The density measured on samples of a few cubic millimeters is in the range of 5 x 10^-2 g cm^-3 with cell size of the order of 1 mm. The conditions which greatly enhance homogeneity and uniformity of the foam will be described. The method is well suited to a mold cavity assembly in which microspheres of 80--100 mm have been coated with foam thicknesses of 200--300 mm