HEPA filters are what trap small particles like PM 2.5, and they’re not expensive! We buy ours straight from the factory so we can pass the savings on to you. Our HEPA size is 296 by 296mm and the thickness is 23mm.
We ran tests using our Original DIY purifier, and found that you should change your filters after around 140 days (in Beijing air). This means a pack of 4 HEPAs should last you a year.
4 filters & pre-filters (to last you a year)