This is surprising to me. I thought the air in the car heats because the interior surfaces are warmed by the sun through the glass, or the exterior of the car absorbs the infrared radiation and transfers that heat to the car's interior. I don't see how moisture is involved in the process.
The moisture is only part of it. However, given good airflow (for heat transfer), the interior of the car will be the same as the air outside. thermodynamics - Heat in the car during sunny day - Physics Stack Exchange
Thanks William, very good post. The "Heatshield" I bought from the Prius Chat Shop claims to reduce the interior temp "by up to 40 degrees." Not quite sure that's true. I bought one for the front and the rear window. It seems to be a pretty good sun deflector, but it still gets darn hot inside. (But I suppose it's better than nothing.)
