Edit: I'm not that familiar with radiation and its parameters/properties. My assumption was that it would accumulate heat. I'll go look up if radiation is a function of heat, then I suppose it could become stable at some temperature. It's surprising to me that you can block out some of the sun from a good area on the earth and not have melting bits.
* Aluminum, Magnesium, Titanium, Berylium
* Graphite/epoxy, Aramid/epoxy, Glass/epoxy
https://www.sciencedirect.com/topics/earth-and-planetary-sci...
I would just use a giant array of solar PV panels as screen, then build a huge coil gun nearby and use all that energy to deflect potential dangerous asteroids by throwing them projectiles made of collected and recycled debris from decommissioned satellites.
This is (very) stupid.
The sun-side of this parasol will be all melty, while the shade side will be extraordinarily chilly. Whatever it is made of, will need to withstand that extreme thermal gradient.
If the temperature of the moon is anything to go by, it's hot but not too hot. According to NASA:
>Temperatures near the Moon's equator can spike to 250°F (121°C) in daylight, then plummet after nightfall to -208°F (-133°C).
https://science.nasa.gov/moon/weather-on-the-moon/
Something like aluminum foil should work fine.