Two layers, one sheet
The parchment side
Touches the food. Silicone-coated paper that nothing sticks to, so fish, cheese and pastry come away clean and the pan stays clean too.
The foil side
Faces out. Folds to shape, seals a parcel tight, holds heat, and blocks light and air for the freezer.
Parchment towards the food, foil facing out. That is the only rule.