CR Boxes

From Covid Wiki

Corsi-Rosenthal Boxes (CR Boxes) are a design for a do-it-yourself air purifier that can be built comparatively inexpensively. They were created by C CR Boxes consist of four or give MERV-13 filters and a box fan or a set of PC fans due to their high speeds and low noise. One of the easiest to build is the Mini PC Fan CR Box by Joey Fox.