I used Space Blankets when they first came out.
They made a heavier wieght like a groundsheet.
I had no money as a 16 year old kid (a long time ago), so I was backpacking using a Tarp and a Space Blanket
The Tarp was a small lenght of sealed nylon with some plastic clip on grommets, and I used the Space Blacket as a ground sheet.
One time I swapped, and put the nylon on the ground and the Space Blanket as a tarp.
I was much warmer that night, and continued to use the Space Blanket as a tarp reflecting my heat back to me.
The small pocket sized Space Blanket was always a required part of the Emergency kit of school hill walking trips.
The kit for being benighted on the hills was/is a plastic bivi bag, which is a heavy gauge plastic bag and a Space Blanket.
The Emergency/Bivi bag was pulled over you and your backpack, and you sat on your backpack for a safe 'dry' night, uncomfortable and also damp from the condensation of the plastic.
The small Space Blanket was used as a personal wrap, like a blanket, and kept you much warmer.
Much warmer than wrapping yourself in nylon like a poncho.
There was definitely reflected heat, not just a vapour/wind barrier.