CCF pads

They are "waterproof" but that doesn't mean they don't hold water on the pad. I keep mine inside my pack liner for that reason.

I agree that the material doesn't absorb moisture due to its "closed cells". The surface does get wet, however.

Some pads have a shiny surface, some have foil covering one side and some have a dull unshiny surface. The latter collect the most moisture on the surface and are hard to wipe dry. Often the cheaper ones have the shiny surface.

Also, if it is too wet for your liking you can always slip the pad under the floor of your tent or ground cloth, whichever you use.

I don't cover mine when I'm backpacking but being rolled up helps reduce the moisture build up a bit.

Ive had my thermarest z lite on the outside of my pack on days full of rain. The actual pad didnt absorb any moisture but it was still very wet. Lay it out when you get to camp in tent or under tarp and wipe off with anything you can. Let it dry a little more and then come back again and do the same thing and it should then be dry enough to lay a sleeping bag on.

Just shake it off, a little water on it is not going to kill you. They do not absorb water.

That's why I use a poncho rather than a Gore-tex jacket: not only does it cover me, but also my pack, keeping everything dry. Even though the CCF pad is waterproof, having it totally dry when it's needed is a nice thing! Also, I doubt that your pack is waterproof (seams), so you'll want a pack liner (garbage bag) to keep everything inside dry. Wearing a poncho in the rain is just added insurance. And to complicate things even more, I've been known to dispense with the poncho altogether and use an umbrella instead.

Happy trails!