IMHO, they work VERY well, as does window tinting.
It's basically the difference between standing in direct sun and standing under the shade of a tree. The ambient temp is the same, and it's going to build up in the vehicle no matter what you do, but, with the sunshade, you do not have the direct sun beating directly into the vehicle, much of the heat is deflected.
You can test this theory yourself. Buy a sunshade. Sit in your car without it, how do you feel? Install the sunshade and sit in the car, feel a difference?
I bought one of the "figure 8" style ones, it's two round hoops sewn into the sheet that covers the window. Each hoop is about two feet in diameter, but you can fold it into a circle that is about 8" in diameter for easy stowage. It takes a bit to figure out how to fold it up, but once you've got it, it's super easy to get it out of the window and stored inconspicuously wherever it is supposed to live. If you're like me, you simply pull it out of the window, fold it in half and toss it in the back seat.
It's basically the difference between standing in direct sun and standing under the shade of a tree. The ambient temp is the same, and it's going to build up in the vehicle no matter what you do, but, with the sunshade, you do not have the direct sun beating directly into the vehicle, much of the heat is deflected.
You can test this theory yourself. Buy a sunshade. Sit in your car without it, how do you feel? Install the sunshade and sit in the car, feel a difference?
I bought one of the "figure 8" style ones, it's two round hoops sewn into the sheet that covers the window. Each hoop is about two feet in diameter, but you can fold it into a circle that is about 8" in diameter for easy stowage. It takes a bit to figure out how to fold it up, but once you've got it, it's super easy to get it out of the window and stored inconspicuously wherever it is supposed to live. If you're like me, you simply pull it out of the window, fold it in half and toss it in the back seat.