Filter v microfilter

Looking over a few things, I note that companies advertise water filters and water microfilters and water purifiers.
As I understand, a purifier uses (toxic) chemicals to kill the bugs while a filter simply screens them out.
BUT, what is the difference between a “filter” and a “Microfilter” other than the size of the screen?
And when does a filter become a microfilter?
Considering the size of most bacteria and proterozoans, a 0.2 filter is more than enough with a 0.3 being mostly ok. At least I know of nothing common that can get through a 0.3 (katadyn) so why get a 0.2 (MSR)?

Sounds like marketing hype. Now there are some filters that can filter out viruses while most cant.

It depends on where you are going. There are .1 filters for use in the tropics… Kataydn uses .2 for at least some of its models.

I finally got a reply from MSR re my Sweetwater.

  1. the color difference in the Sweet5water is simply whatever color they have on hand. the filters are exactly the same.
  2. the difference between the Microfilter and the Purifier is a bottle of bleach in the Purifier box.
  3. the difference between a Filter and a Microfilter is what it will strain. Your screen door and handkerchief is a filter. Once it gets down to 0(point)# microns, they call it a MICROfilter.
    Generally speaking, the smaller the filter, the harder to pump.

A no brainer when you think about it but it is nice to have the official reply.

The crème de la crème @ 0.02 microns the MSR guardian is the ONLY filter & purifier all-in-one.

Technically “micro” refers to anything in the micrometer or sub-mm range (1mm=1000micrometer (um)) range. If they use size terms then they are talking about a true filter based on excluding things of a certain size. If they talk about purifiers then they are generally talking about using chemicals to kill stuff. But not always. The Sawyer Mini filter and other common filters, for example, use a 0.1um filter (or 100nm) which filters out bacteria and big nasties. Viruses are typically 0.02um, or 20nm and above, but viruses are not commonly found in North American fresh water. If you used a 0.02um filter it would plug up long before you had enough water to drink a few drops from most fresh water sources, unless it has a large surface area. So a 100nm or 0.1um will filter out most everything based on size either passing through a filter membrane or through a series of porous tubes. A filter membrane will plug up faster. Porous tubes have much greater surface area and will take longer to plug up. Plus, if filters use hollow-fiber/porous tubes, they generally are in a U-shape so they can be back-flushed and re-used if they plug up. I don’t represent any manufacturer but I did record this video last year. I also own the MSR MiniWorks filter but it is not so convenient to stick in the pocket of a life jacket.