chief, aluminum foil is fine, don't listen to the mindless dribble against it. mylar is just plastic coated aluminum foil.
a member of this site did a test to measure reflectivity which confirmed everything i said in this thread:
https://www.rollitup.org/newbie-central/8102-aluminum-foil-may-your-light.html
the test is on the last or next to last page.
"hotspots" are STILL just a wives tail with no science to back this almost funny claim up. if you really could concentrate and strengthen the energy of light beams with aluminum foil we should be using it to direct super powerful solar rays onto solar panels to create even more clean energy.... the pentagon would be using sheets of aluminum foil on satellites to burn people from space.. lol, it's funny how blindly people take in whatever they hear sometimes.
hey, it's up to you. donate to the mylar cause or keep your money and do something cool with it but at least you have correct info now.