Galvanized Steel Pleat Support-Prevent Rust- How many pleats have you seen with rust flaking off the grid.The HD expanded metal pleat support grid is made of galvanized steel for maximum rust resistance. The metal grid maintains pleat shape and prevents fluttering in operation. Consistent pleat shape minimizes resistance and improves dirt loading characteristics throughout the life of the filter.100% Adhesive Application-Ensures Filter Integrity- The inside of the die cut frame is completely coated with adhesive to ensure a solid bond at all points of contact. The die cut boxes are bonded to reach other. The media pack is sealed inside the frame and the pleat tips are bonded to the diagonal support members.