ok heres something to think about
take a hand mirror and take something painted flat white and go outside in the sun and see if the flat white thing reflects more light than the mirror
I havent tried it yet but im willing to bet the mirror reflects more light and can reflect it much farther. the reason you can see yourself in a mirror in the first place is because it reflects light so well. I can garantee if you compare your reflection with a mirror vs. mylar that you can see yourself much better in a mirror. if a mirror sucked in so much light you wouldnt be able to see yourself in it. kinda like a black hole that sucks in light. you just wont be able to see it because it sucks in all light.
maybe I will try some side by side experiments.
plus another thing I noticed is that with mylar is that it reflects hot spots where the flat white wont so that to me kinda makes mylar like a cross between aluminum foil and a mirror.