ok - just got off the phone
I have a chum who works at alcan enfield alloy (makers of bacofoil)
the foil is shiny only on one side - because the dull side slightly scatters the heat and thus conducts it better
(if it was shiny on both sides the package would reflect in both directions and cause hotspots on the food).
shiney IN ... the dull collects the heat and transferrs it uniformly - the shiny then keeps the uniform "layer" of heat in.
cold doesn't reflect in the same way - so it doesn't really matter (shiney out goes with the roll) ... but the conduction will help prevent frost burn.
if you put a tenner on a 50p coin and then hold a fag end on it it won't burn (dull side - conduction helps) - good for ironing