"These are the best filters available...One of the best purchases I have ever made," says Henry from Montgomery, Alabama. Well, thanks Henry! The minute you take the filter out of the box, you will realize it is special. The Ultimate Air Filter is unique in that it has electrostatic properties while containing no polyester. Instead, it contains a unique 5-layer combination of Polypro with Polyurethane foam media. This gives it very low air resistance and makes it super easy to clean while maintaining a dust arrestance rating over 90%. The filter is designed to build a natural electrostatic charge (no electricity required) that attracts and holds dust like a magnet. The frame is made from heavy duty aluminum and the screen is black plastic grid. This filter has a white side and a black side and unlike our other filters, it is one-directional. An arrow located on the outer frame lets you know which way to install it. The Ultimate Air Filter is made from premium materials and costs a little more to produce but we are confident that, like Henry, you will consider it one of the best purchases you have ever made.