A hollow fiber membrane is formed by embedding a braid having a spiral open weave of monofilaments only, to avoid a whiskering problem. The open weave is characterized by contiguous, circumferential, rhomboid-shaped areas of polymer film separated by monofilament. When the braid is supported on a plasticized PVA cable having a scalloped periphery, the braid can be infiltrated with membrane polymer which, when coagulated, embeds the braid positioning it around the lumen. The embedded spiral weave, free of any circumferentially constricting monofilament, allows the membrane to be biaxially distensible. The membrane has give not only in the axial or longitudinal direction but also in the radial direction. Give in the radial direction permits soiled membranes to be backwashed under higher pressure than in a comparable braid which is not radially distensible.

Method for making multiple durometer bulb seals and any other types of multiple durometer seals and moldings includes cooling separately at least one structural member and at least one sealing portion, which have different durometers and shapes. At least a first extrusion is drawn through an extruder, forming a structural member profile and the extruded material is pulled along a longitudinal axis to a first calibrator device and first cooling tank to cool the structural member profile to a predetermined temperature. Cooling medium directly contacts the outer and inner surfaces of the first profile. Downstream, the sealing portion is extruded and affixed onto the cooled structural member and pulled further downstream to a second calibrator device and through a second cooling tank to cool the final profile a predetermined amount. Disparity in cooling expansion and cooling differential between the multiple durometers and shapes is avoided or overcome.

A hollow fiber membrane is formed by embedding a braid having a spiral open weave of monofilaments only, to avoid a whiskering problem common in prior art multifilament braid-supported tubular membranes. The open weave is characterized by contiguous, circumferential, rhomboid-shaped areas of polymer film separated by monofilaments. When the braid is supported on a plasticized PVA cable it can be infiltrated with membrane polymer which, when coagulated embeds the braid positioning it around the lumen. The spiral weave, free of any circumferentially constricting monofilament, when embedded in film, allows the membrane to be biaxially distensible. In other words, the membrane has give not only in the axial or longitudinal direction but also in the radial direction. Give in the radial direction permits soiled membranes to be backwashed under higher pressure than in a comparable braid which is not radially distensible.