Really off topic

Dull side up
shinny side will reflect the heat a bit more
 
Depends if the food is under or over the tin foil.
 
Why would anyone cook tin foil?
 
Not sure, but for tin foil hats, the shiny side should be up to better reflect the rays from outer space.
 
Actually, there was a study about this a while ago (yes, someone anal enough to study this) and the outcome was that it didn't make a difference.
 
I used to use tin-foil a lot for cooking. I don't remember why or how.

</Alzheimer's>