air permeability of the tricot is ranging from 1 to 20 cm 3 sec cm 2 and in this embodiment air permeability of tricot between 2 to 5 cm 3 sec cm 2 is preferred to use the thickness of the tricot substrate should be between 100 to 500 microns and preferably between 250 to 400 microns the density of the tricot substrate should be between 50 to 200 gm per sq meter and preferably between 100 to 150 gm per sq meter since tricot substrate is a close knit design with fibers running lengthwise while employing an interlooped yarn pattern where one side will feature fine ribs running in a lengthwise pattern while the other side may feature ribs that run in a crosswise direction it should have 5 to 30 wales per cm on the rib side between 10 to 15 wales per cm is preferred in addition on the smooth side of the tricot it should have 5 to 40 courses per cm between 15 to 25 courses per cm is preferred in this invention the total thickness of the u201c cast on tricot u201d asymmetric or composite membrane should be 400 to 800 microns preferably between 500 to 650 microns in accordance with the preferred embodiment of this invention the u201c cast on tricot u201d membrane is fabricated by casting the polymer dope to form a thin layer of solution on the tricot substrate precipitating the membrane in low or ambient temperature water ranging from 0 to 25 u00b0 c typically at about 0 u00b0 c is.