How to cook with tin foil
There seems to be great debate about what side of tinfoil – shiny or dull – to have on the outside when covering food for cooking. Point is, it doesn't really matter as both sides will do the job when roasting or baking a dish – because oven temperatures are so high, the heat will penetrate the foil no matter which side you choose.
So the old adage that the shiny side reflects heat creates only minimal difference. In fact, the different appearances of the two surfaces are simply a result of the manufacturing process.