A little off-topic, but the below post reminded me of something I did recently...
"To create a cool shadow under a cuben (or other) tarp or shelter in warm conditions I drape my quilt or sleeping bag over it. Casts a cool shadow and airs the quilt at the same time."
I did something kinda' like this recently with my Spinnaker tarp: I was on a late summer trip in high temps (low 100s F) that we ultimately had to bail on and hike out to a TH. This being chaparral country, there's no trees to get in the shade of, so while waiting for a ride I pitched my tarp in an A-frame configuration somewhat high off the ground to allow better air circulation and then used an SOL Emergency Blanket (made of metalized polyethylene) to drape over the roof of the tarp (metal side facing the sky) to reflect the heat and create shade.
It was certainly still warm, but it seemed to somewhat help as it was noticeably cooler under the tarp as compared to sitting out in the full sun.
The Emergency Blanket is primarily used as my groundcloth. Weighs ~2.5 oz, costs $4.00 and is the perfect size for one under a tarp. Added bonus: It can double as an... emergency blanket. And now shade structure.
I suppose had it been windy, I would've needed to tie off some cord to the corners of the blanket and secure it to the ground to stay put.