I've used the cardboard kind (they worked fine if you have the right size), the tinfoil coated ones (worked till the clear started flaking all over my car), but in my VX now I have one that is made of some kind of nylon (maybe brushed nylon) and in it are two wire hoops that are almost the heigth of the windshield. The material is actually rectangular and fills my window space quite well, and when it's not in use, you just fold it in 1/2 (the two hoops on top of eachother), then by holding each side and twisting them, they go into a smaller 8" diameter circle for storage. Just another option from many out there.