Many/most small PSK will include a mylar "space" blanket or a plastic sheet. I was wondering, if I needed to rig a sun shade to protect me from the rays of the summer sun while I rested during the heat of the day, would one material be preferable to the other?

Seems like the mylar would be the winner since it is not only opaque but also reflective, but maybe in actual use, there's little practical difference. Was wondering if anyone had any practical experience with this. I'm thinking of a worst case scenario like being in a semi-arid or desert region with no natural shade, like trees or geological features, so I would need to dig little trench, hopefully to find cooler ground, then put the sheet over the hole.

Thoughts?