All I know about aluminum besides the basic facts is that it dissapates heat very quickley. If you take amuminum foil out of an oven, it doesn't stay hot for very long. I don't know if this is good or bad for a heatsheild but it does keep out the hot air. honestly, I did it more for asthetics (even though my particular example is not that sexy) The difference between heat sheild and no heat sheild is negligable. it won't shave any time off your 1/4 mile nor will you notice it in day to day driving.
