A filter of the type incorporating a porous filter membrane1. Frequently such membranes are very fragile, and the invention described an improved way of mounting them within the housing. Attached to a perimeter portion of the membrane 1 is a thin strip 8 of flexible material such as polypropylene. The strip 8 is attached, on the one hand, to the base 4 of the filter housing by a first joint 10 and, on the other hand, to the perimeter of the membrane by a second joint 9. Between the two joints is a region of flexure which enables the membrane to float relative to the housing, thus isolating the membrane from relative movement between the membrane and the housing.