Which is cooler, the front seat or in the trunk? No, I don't mean which seat is more desirable on a trip to Las Vegas, I mean which place is literally cooler? Which spot is least likely to melt your tealights, wilt your flowers and blacken your Ryan Adams tickets? 

Inspired by a need to store boxes of See's Candy in my car for a few hours, I tried a few different spots, settling on two areas in particular:

1) on the floor, in front of the front passenger seat. 
  Some direct sun would probably hit it, but it would be mostly in the shade. 
  The windows could be open a bit, allowing the hottest air to escape
  The abundant windows would let a ton of sunlight into the car, heating the interior.

2) in the trunk
  No direct sunlight
  No indirect sunlight
  No openings for the hottest air to escape.

I should specify, I wanted to know which was cooler when the car was parked in the sun, for four hours, with no air conditioning?
Which one would provide a safer enviroment for ice cream? If the trunk was cooler for groceries, wouldn't it also be better for pets?

But enough conjecture, and on with the experiment. Frozen food trucks and shipping containers have a special thermometer which marks the highest and lowest temperatures experienced during the voyage. 

Two of those thermometers would answer my quesitons. But I didn't have two of these thermometers.

Instead I'd be using 20 pound bags of ice. At lunch I drove to the store and bought two new bags. One went in the trunk, the other one went on the floor inside the car. I parked in a sunny spot on a hot day, windows cracked open about one inch.

I'd wait til the end of the day and weigh whatever ice hadn't melted away. The temperatures themselves didn't interest me as much as which position melted the most ice.

In four hours, I was ready to weight whatever was left. If both bags were completely melted, the experiment would be ruined. Luckily, only about half of each bag was gone. 

I punctured a hole in the bottom of the bag on the interior floor and let the liquid run off. Water continued to drip as I hoisted it onto the spring scale. 12 lbs.

Next I weighed the bag from the trunk, remembering to drain the water first. 10 lbs.

Aha! There was my answer. In the trunk, ten points of ice had melted. In the can interior, even with some of the bag in the direct sun, it was still cooler than in the trunk.

So, there is your answer! Whether you are keeping ice, flowers or vinyl in your car, the interior is a cooler place on a hot day. I hope you put this knowledge to good use.