Compared to porous PP membranes, where gas molecules can freely permeate through, PMP membranes possess an asymmetric sponge-like structure with a dense hydrophobic outer skin. The high porosity and uniform pore distribution in the membrane's inner wall ensure high permeability of oxygen and carbon dioxide, while the thin non-porous outer skin avoids direct contact of liquids and gas. Thanks to PMP's high intrinsic gas permeability, reduced plasma leakages, and the possibility of operating for several weeks , PMP became the most widely used membrane material for long-term ECMO.