There is provided a filter unit for a smoking article having a tube formed from filter material and the tube having a first portion and a second portion, wherein an inner diameter of the first portion is different from an inner diameter of the second portion. There is also provided a tube having a longitudinal axis, wherein a straight line following at least a portion of an internal or external surface of the tube intersects the longitudinal axis at an angle other than 90°. Also described is a body or tube of filter material having a longitudinal axis, a first end surface and a second end surface, said body or tube formed from a plurality of continuous fibres extending between said first and second end surfaces, wherein the density of said filter material is greater at said first end surface than at said second end surface. A body of filter material is also described having a longitudinal axis and a channel or recess formed in the body of filter material, the shape of said body of filter material having no lines of reflective symmetry, as well as a body formed from filter material, the body having an end surface and a recess formed in the end surface. A smoking article including the filter unit and a kit comprising a smoking article and a filter unit are also described.