Sintered metal filter elements are made from powdered fecralloy which is formed into porous sheets, before being pleated into a traditional-shaped cylindrical element. The major advantage of sintered metal filter elements is that they conduct heat well, so they can be heated directly to initiate regeneration (ceramic filter elements can only be heated indirectly, by heating the exhaust gas first). Once regeneration has started, it spreads rapidly through the filter. A second advantage is that they are better at withstanding shocks and vibration than the ceramic alternative. Sintered metal filter elements can remove roughly 99% of diesel particulate matter by mass and a very high proportion of particles by number. Sintered metal filters can be catalytically coated, which is one way of promoting passive regeneration. If they are coated, they must only be used with ultra-low sulphur fuels.