Well, my mistake, I expected it to be foam but it's the K&N pantyhose prefilter. It actually looks pretty good though, thicker than pantyhose by quite a bit. Hmmm, I wonder if I could use some No-Toil motorcycle filter oil on it and solve the microdust problem with finality?

The air filter Mike Caskey used is HUGE, so maybe with less demand on each square centimeter, plus the prefilter, it might work out as is.

I also thought about a tube paper filter, like from a Cosworth Vega. I could fab up a connector for it fairly easily. I could also just extend the tube into a homemade snorkel and run the filter on the top or something. Hmmmm. Need a splashguard of course, but... hmmmmm....... fab an airbox, snorkel..... hmmmmmm......

That No-Toil is pretty fabulous stuff by the way. Not sure I would use in on a K&N unless I had one to burn. It's water cleanup with their activator (USE GLOVES!), but really made for foam. Making a foam sock, or using a UNI filter as a sock, would work nicely. UNIs are reputed to pass microdust too though. But the foam on my XR650R is QUITE effective. Hmmmmm....