Abstract: In certain operating conditions of diesel engines, diesel soot filters which are made of known ceramic foam and filter efficiently per se have zero or only a very low degree of particle filtration, in particular at hight exhaust temperatures and exhaust velocities, that is, above all when the diesel engines are running under full load. Ceramic foam filters for cleaning exhaust gases of diesel engines in which the surface is roughened and wherein the peak-to-peak interval is approximately 1 to 100 .mu.m, preferably 1 to 10 .mu.m, do not have this disadvantage. A ceramic foam of this kind is manufactured by roughening the surface by deposition of inorganic materials and, if required, subsequent decomposition by temperature treatment.