I picked up 12 mylar emergency blankets for ONE DOLLAR free shipping on ebay, one would line your entire box....using a. foil is not a good idea, (I used it in my first small grows just like everyone else) you have sooooo many cost effective options that are so much better, I mean seriously, paper from your printer, flat white plastic, a can of paint, MYLAR BLANKETS, better reflectivity and no hot spots, youll never use it again once you fry a branch and stunt your plant a week or betters worth of growth.
Mylar blankets are only marginally better than A-foil.
You may want to re-evaluate how you're using them.
Every crease in the M-blankets throws your light at all kinds of crazy angles, mostly away from where it's useful.
Plus, they're see-through! Meaning some of your light is escaping. Hold one up in front of a light and you'll see right through it.
Do they reflect light? Sure.
They're more efficient though if you glue them to cardboard, without any creases of course, and make panels instead of simply hanging it.
I've learned through the years that
most "hot spots" are a figment of the indoor gardeners imagination, and usually just a poor excuse for lazy garden maintenance.
Indoors, we're trying to mimic the outdoors. Unless you use a light mover you MUST rotate your plants if you're using HID's. If not, it's like (outdoors) aiming a magnifying glass at your stationary leaves. They
will eventually burn.
Tube Flouros and CFL's will rarely burn your leaves. That is, unless user-errors come into play, like having them too close.
Proper lighting is another matter of personal gardening skills, or lack there of. People mess up and blame it on everything but themselves. That's how all these myths and rumors get started and perpetuated.
Don't blame your equipment - blame yourself when you Eff-up.
*EDIT
This post isn't directed at any one in particular. Sorry, but I suck at talking in "3rd party".