@abhayakara@mastodon.nl There are also variants on this CR Box design which use other filters which are more available in other regions. For instance, you can use the Starkvind filters from IKEA in the same box shape with PC fans mounted to a piece of cardboard, foamboard, plywood, etc. on the top. A web search for CR Box Netherlands or CR Box Germany will show you some examples of what materials and methods others in your area have used.