Abstract: A filter cell for use as all or as part of a filter panel includes an upper face 1 and a lower face 2. The upper face 1 and lower face 2 includes a set of parallel ribs 3 interconnected across one end by a further rib 4 orthogonal to the ribs 3. A mesh panel 5 is provided between each of the ribs 3 to define a flat surface through which air or gas can flow. The ribs on the upper face 1 cooperate with the ribs on the lower face 2 to define a plurality of open ended compartments spacer frame 6 which increase the size of the compartments by extending the ribbing 3 on the upper 1 and lower 2 faces are provided between upper face 1 and lower face 2. The upper face 1, spacer frames 6 and lower frame 2 are assembled by snap-fit using corresponding male 10 and female 11 lugs. A filter medium is inserted through the open ends into the compartments and a slide plate is used to close the ends.