moulded from a non deformable thermoplastics material such a polyurethane by non deformable it is meant that any deformation that may take place when the roll cover is in use on a roll would be minimal such that fluid passageways 8 provided in the roll cover remain open thereby not hindering the dewatering of the stock referring to fig2 the membrane comprises circumferentially straight yarns 5 embedded within the thermoplastics material the yarns are in the form of a high shrink yarn with a polyester core the diameter of the tube 2 of formed membrane is supplied slightly larger than the diameter of the forming roll to which it is to be applied such that the membrane sleeve 2 can be easily installed onto the roll once in position on the roll the membrane is then heated with an infrared heater or steam in order to shrink it into tight fitting engagement with the surface of the roll the embedded yarns are shrunk at the same time providing a structure which is less likely to yield thereby increasing stability and preventing the membrane from loosening the membrane 2 thereby forms a shrink sleeve with a non marking seam within its structure the planar surface with apertures 8 allow water to be drawn through its structure into the forming roll to increase dewatenng of the paper web entrained about the forming roll between the forming fabrics in the embodiment illustrated in fig1 the members 4 and 6 are respectively aligned along the machine direction and cross machine direction however the members 4 and 6.