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I'm guessing you were directing this at me? I wish I had an easier way to post pictures. The underside is pretty soft. It's not exactly "felt" but is a white textile/fabric. It could be cotton, I'm not sure. The soft layer is not very thick, but enough so to where it slides easily across the car when pulling it on or off.
I imagine it's possible that sand, etc... could get caught in the fibers of the underside and cause scratches to paint, but I've not had that happen. It seems pretty waterproof as well. The rear spoiler makes it trap water after a rain, and I haven't seen any make it through the cover, even after a couple days.