What kind of aircraft? There are a number of options available at different price points but depends entirely on type of aircraft (construction, AB/E vs TCd, etc.).
My preference is to use an FAA certified material even if it more expensive - I certainly want something that is flame resistant. This is for a certificated plane - Bellanca. Construction is fabric over tubular steel.
The materials I've seen work the best in both airplanes and helicopters come from Soundex and Soundcoat. Have installed both, but they're not cheap. Keep in mind how well the soundproofing works also depends on its installation. So if installing on removable interior panels, how those panels are installed becomes just as import. Both OEMs above were helpful in selecting the right material and tips. I'm pretty sure Air Spruce still carries Soundex products but I ordered direct from Soundex. And as a side note, another sound/vibration generating item is an out-of-balance prop and/or worn rubber engine mounts. It's strictly optional, but having your prop dynamically balanced plus comparing the vib spectrum from the engine to the airframe may also help smooth/quieten your ride.
Yup - that's the same stuff as I used in the cherokee while it was down for engine overhaul. Not sure if I used the same thickness, but it's FAA approved and all that. Definitely reduced the noise and as an added bonus, makes the interior a bit less frigid in the winter weather (which just hit Denver yesterday). I also added a layer on the back side of the back bulkhead.
Any issues with trapped moisture?
nope
