the present invention is a hollow fiber separation assembly having one or more bundles of hollow fiber membranes with a tubesheet at each end enclosed by an end cap . an impermeable housing , preferably made from a flexible polymeric material , most preferably a shrinkable tubing , contacts and encloses the bundle , extending between the end caps . the polymeric , impermeable housing contacts and compacts the array of fibers in the bundle to enhance axial flow along the outside of individual fibers , protects the fiber bundle between the end caps , and contains the permeated fluid and diverts it to a port or ports at the end of the bundle . this hollow fiber separation device provides a large capacity , and is also low cost , lightweight , may be used as a stand - alone separation device , and does not have a high - pressure section which requires testing .