The reflective tarps are not breathable. But you just need to use that to block the sun out, you can use the cotton on other sides for air flow. Get creative.
Think of an upside down refrigerator cardboard box. You would want to cut holes out of the bottom and maybe some up top for air flow. But if you put the tarp 2’ above the box, it would never restrict air flow, just block the light from the box.