Is the top cover just a nylon material, or is it that material that makes a crinkling noise that is used in so many cat toys? My son's cats would love it, but only if it's not crinkle noise material - they are scared to death of that. They even go scurrying when they hear a plastic grocery bag! They've been with us since they were just babies, and no one here ever scared them with a noisy bag, so we don't know where that fear comes from. Go figure - just a silly cat notion I guess.