Pall rings are a type of open-ring packing with equal height and diameter, developed on the basis of Raschig rings. Each layer of the window openings has five tongue-shaped leaves (plastic Pall rings are connected to the center in a "井"-shaped or "米"-shaped pattern), with each leaf curved inward toward the center of the ring. The window openings of the upper and lower layers are staggered opposite to each other. Generally, the open area accounts for about 30% of the total wall area of the ring, allowing gas and liquid in the packing tower to flow freely through the window openings. This improves gas-liquid distribution and makes full use of the inner surface of the ring.