Wow! That is some eye opener! I had a sneaky suspicion about this being true beforehand since I have one of my CFL's with an aluminium foil reflector and the other with a much more reflective foil material (not mylar). It seemed like the aluminum foil side was a tad brighter but I thought it was in my head. Still, it might be that optimized reflectors (correct geometry and size for the bulbs) might still work better with Mylar as compared to aluminum/white paint.