There's no hard and fast answer. It all depends.
Shiny side out offers better basic reflecting power, but shiny side in scatters the rays better. If you're among friends, I'd go shiny side out, but I'd reverse that when travelling in a hostile environment.
Likewise, on the inside, shiny-side-in serves as a natural intelligence-booster, whereas fuzzy side in works as an aphrodisiac.
As to my personal preference, I usually do two layers and go double-shiny.
Thank you, that makes a lot of sense to me. I feel better already.
There's no hard and fast answer. It all depends.
If tinfoil is scarce, a gallon sized ziplock bag and about 10 feet of plastic wrap tightly wound around the head will keep easedropping parties from hearing any more conversations on the transmitter in your fillings < /sarcasm >