HEPA filter. Compare to part number 40140201. I needed an inexpensive scrubber/air cleaner, I couldn't afford the hundreds of dollars for what I needed. I need a HEPA filter and activated carbon. I 3D printed an enclosure that includes a HEPA filter and activated carbon. I bought a 7530 75mm x 75mm x 30mm 5V USB Blower Brushless Cooling Fan ($12), Activated Carbon (5£20) and this filter set ($15.99 for two). What I got was a SUPER powerful air washer. I only paid $48 plus the cost of the 3D filament, I saved over $300! Thanks for a great product!