The reverse osmosis membranes we supply consist of several thin layers, or sheets, of film that are bonded together and rolled in a spiral configuration around a plastic tube, also known as a thin film composite or TFC membrane. The material of the membrane is semipermeable. it allows water molecules pass through while acting as a barrier to dissolved solids (i.e. minerals, chemical contaminants). When the feed water stream passes across the surface of the membrane, the water molecules penetrate the membrane surface, working their way around the spiral and collecting in the center tube. The remaining contaminants are concentrated and washed from the surface of the membrane down the drain.