Swedish tracing paper works well for a pre-filter. It's inexpensive for a long, seemingly inexhaustible roll, and can be washed numerous times. It also works w

Swedish tracing paper works well for a pre-filter. It's inexpensive for a long, seemingly inexhaustible roll, and can be washed numerous times. It also works well by itself if you just want to cheaply filter large particulates. I used to use it in those cheap $40 Hamilton Beach air purifiers. The OEM filters for those cost almost at much as the new unit and wear out [for me] within a couple of weeks. That setup with Swedish tracing paper works well for dust, as a supplement for my HEPA filter purifier.