At the risk of loosing our inner geeks, I’m wondering whether a decrease in pore size from .2 microns to .1 micron makes any practical difference for backpackers?

I realize that a smaller pore size means smaller gazigglies get filtered out. What I’m wondering is whether there are any significant numbers or types of harmful stuff that would make it through a .2 micron filter that a .1 micron filter would stop.

In practical terms, probably not, since giardia and cryptosporidium cysts are quite a bit larger. Not sure about other nasties.

Also, keep in mind the difference between nominal and absolute pore size. Manufacturers sometimes specify, sometimes not.

A nominal pore size rating refers to a filter capable of preventing passage of a minimum percentage (usually between 60% and 90%)of solid particles of greater than the stated pore size.

An absolute pore size rating specifies the pore size at which a challenge organism or particle of a particular size will be blocked by the filter with nearly complete efficiency (greater than 99.8%) under strictly defined test conditions.

My inner geek thanks you

Sawyer claims their 0.1 micron filter removes a higher percentage of stuff than larger filters.

https://sawyer.com/water-filtration/

That is probably true, but my understanding is you don't need just one nasty to get sick. You need enough to overcome your bodies defense mechanisms. As result, the number of 9's after 99.9xxxx% probably does not make a big difference in your chance of getting sick.

You'll notice at that link above, Sawyer sells filters at 0.02 microns which they claim can filter viruses. If viruses are a big threat in your water supply (i've heard tropical countries) then that might be a good filter to have.

IIUC bacteria sizes vary so the smaller pore size will filter out more and smaller bacteria. It will also make the filter more susceptible to clogging, which can be an issue depending on one's water source. Will likely slow the filtration rate as well.

Cheers,