I often hear that fur, yarn, wool hold water when it raining...and its usually stated as a negative toward the silencer only.....like nothing else gets wet or is effected. Rubber silencers hold water too.
When its raining I pluck my string occasionally to clear the water from my WHOLE BOW....yes, the water on the silencers...the water that is beaded up on the sting, the limbs of the bow, and the shelf/rest area. The silencers, no matter what they are made of, are going to be effected by water,...but so is EVERYTHING ELSE.
You should always strive to keep your arrows n feathers dry....and keep you bow clear of water by plucking your string.