The Corsi–Rosenthal Box is a design for a do-it-yourself air purifier that can be built comparatively inexpensively. It consists of four[1] or five[2][3] HVAC particulate air filters that form a cube and a box fan to draw air through the filters. The seams of the cube are sealed with duct tape. A 2022 study found the clean air delivery rate on the five-filter design was between 600–850 cubic feet (17–24 m3) per minute (depending on fan speed), costing roughly a tenth of commercial air filters. Engineers Richard Corsi and Jim Rosenthal created the five-filter design during the COVID-19 pandemic, with the goal of reducing the risk of infection by reducing the levels of airborne viral particles in indoor settings.
You can read more here: https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box
