Chad addresses the issue of the greenhouse effect in your car, and whether putting a sunshade inside or outside matters: Greenhouse Physics and Car Shades
In the first comment we find the following question
Does car window glass block IR?
to which Chad answers
I like the idea of testing this with a piece of glass and a heater. You could probably do it with a toaster or an electric stove and a Pyrex baking dish (don’t put the dish directly on the burner, though, because they can explode that way)
Here you go. I had a beaker rather than a baking dish, and I used the IR thermometer I demoed a few months ago
You can see that the filaments are heating up, but when the beaker is put in place, the temperature drops to ambient. So it blocks basically all of the IR in the region of sensitivity of the device.