I've been doing some more experiments the past couple of weeks, and found a couple of ways to reduce the temperature in the trunk of my Ford Escort.

(See my previous posts for previous results.)

With no protection, the trunk area gets 30-35°F hotter than the outside temperature when sitting in the sun all day.

With an old reflective sunshade laid on top of the rear deck, the trunk temperatures were only 15-20°F warmer than the outside temperature. But that occasionally produced bright glare on the inside of the rear hatch, interfering with my view when I change lanes. And that's unacceptable.

So I laid an old white towel over the sunshade. And the temps were still only about 20°F warmer.

Finally, out of curiosity, I tried it with just the towel. And it went up to 20-30°F warmer.

While it wasn't as good as just a sunshade, the sunshade with the towel over it was the best acceptable combo. I'm sure the air space produced by the sunshade (it doesn't lay flat in the area available) contributed to that.

So that's the final result. In my old, battle-scarred little Escort, the towel over the sunshade on the back deck doesn't look bad, and keeps the trunk a little cooler. It also gives me an easily accessible towel, and we all know that's important!