Small, open-ended; parylene microcylinders of 400 mu m diameter, 700 mu m length, and 10 mu m wall thickness were filled with a solution of a polyfunctional monomer of low concentration. The solution was polymerised in situ with ultraviolet light to produce a gel. Precipitation of these gels in a nonsolvent and subsequent drying by means of a critical point drying apparatus produced microcylinders filled with a low density foam. Radiographic examination of the foam gave a density of the order of 2 mg cm(-3), and scanning electron microscopy micrographs showed cell sizes of the order of 1 mu m. No shrinkage of the foam was observed with cylinders of the dimensions given, but. with larger cylinders of diameter and length of the order of 1000 mu m, some axial shrinkage was observed which resulted in cylinders with slightly concave ends (of the order of 20 mu m).