Okay, this is how I did it:
You need myalr, duct tape, and a staple gun.
The duct tape has to be the rubbery type, not the aluminum sort.
If you are using those blankets, you HAVE to do it this way.

Okay, so first cut your mylar to fit the wall.
Now take your duct tape and tape all around the edges of the piece of mylar you are going to hang. I like to do it so that it is like a taped hem (if you sew you know what I am talking about).
Now you can staple through the duct tape in just a few spots, and it will be reinforced and not rip, and you can yank it down fast, and flip it over and rehang it if it gets too dirty.