I have driven thru down pours at speed and these filter work just file. No moisture is let in to cause hydro lock. This was debated long ago when Rob first started building the single.
+1 to that. The day I installed my CAI, I drove down to Auburn to have the aforementioned maxcichon assist with the install. On the way back home, I ran into a downpour hard enough to make me pull over, it rained the remaining 50 miles almost as hard.
I was concerned, so when I got home, I had a look at the air cleaner - dry as a bone.