Two days ago i recorded thunderstorm. Used plywood with towels as a roof. I liked the result, much better, than without towels. But i feel there is a room for improvement - possibly i'll get some foam or more furry towels. ;-)
The best foam will be quite large-celled and quite open-meshed. You want to break up the drops while allowing the water to flow out easily without saturating the foam. Most small-cell foam, towels, whatever, will saturate over time or in a hard rain and become less effective at damping the energy of the drops.
Foamed airfilter pannels can work well if they are made of water resistant material that won't sog up. I have a roll of black foamed plastic material which is supposed to be used as a pre-filter before the big rectangular paper filters used in A/C handlers. It's supposed to be trimmed to whatever size is needed. What I have is only 1/2" thick or so though, so with something similar you might want to double it up.
Topic: Recording night sounds - how to protect gear from wet? (Read 6914 times)