I got Cal Car Cover (Ultra-weave??) as it was advertised to have "superior resistance to weather" and some other glamorous claims. This was not the multilayer, dimpled cloth type stuff that I have seen, but still was at the high end of the materials offered by CalCovers. Anyway, at Carlisle this year I used it for the first time (car normally stays in the garage at home) and it was surely better than nothing, but still, after a good downpour and overnight rain, the car was wet underneath the cover. I had the top and side curtains up, of course, and there was not any water to speak of actually inside the car, but the car was wet under the cover and some water in the engine compartment. The cover itself was like a wet sheet, not repelling water in any way. I felt as though I had been seriously misled as to what a "Car cover" was supposed to do. I called CalCar and complained, and the very chirpy young lady patiently explained to me like I was a complete idiot that, oh no sir, no car cover is completly water proof, as this would be a terrible thing and would ruin the paint. Their covers, no matter what material one might be made from, will all admit some water/moisture given enough wind/rain applied, and this is just the way it is. They are all supposed to allow the finish to dry (breath) after exposure, and not trap condensed moisture on the finish. As a consequence, thay all admit water through them when it rains hard. So I am stumped, actually. No longer able to decide what would be best. I purchased a patented Gordon Nichols car cover a year ago (also known as as a poly tarp and bungie cords) and used that to good advantage under downpour conditions. All I wanted was to be able to keep rain out of the engine and cockpit when parked outside now and then on trips. Not sure how to achieve that now.