Aluminized Paper Wrapper Sides
It actually makes no perceptable difference as far heat retenion. The paper has a miniscule insulating effect too. Once heat hits foil interface, it is partially reflected.

The paper does absorb some of the fat and liquids from the wrapped contents and helps keep it from making the 'bread' mushy and if the paper is out, you MIGHT have a bit less messy hands or is it the other way around?

Similarly, Reynolds will be the first to tell you that shiney side in or out on foil makes absolutely no difference

End result = it doesn't matter!