How hot does it get in the bed under a black tonneau?

[MarkH13]

I found a thermometer and put it in the bed of my truck with the cover closed and after an hour it read 112. I opened the cover and left it for 30 minutes and it maxed out - it only goes to 120. For reference I have a rubber mat in the bed and the bed is rhino lined. Not sure how much that helps but it is cooler with it closed shockingly. I'm guessing that the carpet lining helps deflect heat.
It is 94 here with a heat index of 107 and sun shining with very few clouds.

 

[Summit1]

The temperature beneath the fully closed cover will vary, based upon the amount of direct sunlight and ambient air temperature outside the bed.

I am tempted to stick the Fluke w/ temperature probe in the bed of my truck while parked in the sunlight to see how hot it gets.

 

[GTyankee]

I had a 1/4" thick steel toolbox in my 2009
It was under a soft tonneau
I had to use gloves to open it, in our summer heat





With my 2016, i had aluminum tool boxes made




Its cooler by far