The other guy isn't technically wrong. But I know from experience that while your car will be warm on the inside, using the shade will mean the difference between unbearably hot and warm.

Just park so that your car points mostly towards the sun so that the windshield has the most direct sunlight and put up the shade.

The reason it works is because the sun gives off IR radiation (in addition to visible light and UV). Glass traps heat when given by IR. The IR passes through the glass, hits the interior surface, then gets converted to physical heat. Which is then trapped by the physical barrier of the window. The cover reflects most of the IR back into the sky. So the car mostly warms up from heat absorbed by the ambient air temperature, instead of being blasted by direct sunlight.

[–] Senshi@lemmy.world 3 points 1 year ago

Exactly right. I just meant that it definitely still will be uncomfortably warm when you get in at first, but overall hear will be lower. So definitely use it!

Preventing the interior from being hit by direct sunlight also has the huge advantage the once you let out the warm air, there are no superheated parts that continue to radiate heat for many more minutes, making the actual ride much more enjoyable as well.