Reflective material a lot better than sheet shade...

[nebulachic]

...for tent?

[gyre]

If you can make it work, yes.
It all needs to block or reflect the heat.
What isn't reflected must be released as heat.
Put your hand under different types.
You can even make a tiny box and set it in the sun and test for temp.
Taylor makes thermometers that hold the high temperature.

[ygmir]

It will also matter if you have an air gap between said shade and tent........
Once the heat " transmission process" is changed from infrared to radiant, (I think I have those terms right, not sure), an air gap can carry a lot of it away.......
Reflective works best for infrared heat reflection. The darker, less light transmitting the shade is, the more is stops infrared and will then allow the air to dissipate the heat absorbed.

that said, it is just my understanding of how things work......your results may vary........

[robotland]

I just made a couple of big solar reflectors by coating sheets of cardboard with 3M spray glue and then laying space blankets on and burnishing them down. A little duct tape to secure the edges, and voila!

...the plan is to zipstrip them to the roof of the car.