At a local shop, I regularly get burritos. They come in a wrapper that is paper on one side and aluminum foil on the other.
They consistently put the aluminum on the outside.
This seems incorrect to me. The aluminum should go on the inside to reflect heat back into the burrito, and the paper should go on the outside so that it doesn't absorb burrito goop.
Am I correct? If so, are these reasons correct and exhaustive? If not, why?
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!
Most food shops likely use a foodservice insulated foil sandwich wrap. By design, the paper side is to be on the inside and the foil side out.
While not all have this design, most that I've seen are like the image, laminated with a honeycomb design. This allows for small air pockets between the paper and foil, increasing the insulation ability of the wrap.
Reasons that the paper goes inside and the foil out:
The paper will absorb any leakage from the food item or any condensation that forms. If the foil were on the inside, it wouldn't be able to absorb it, so any moisture would be absorbed by the tortilla, bread, bun, etc.
Better insulation/heat retention. By having the less porous material on the outside, there is less heat loss.
As mentioned in another answer, the foil may slightly stick to the food item and could possibly tear. This would allow moisture to seep to the outside paper and could be quite a mess.
I am guessing you are talking about something like this:
When wrapped around something hot and breaded (like burrito or a hamburger) condensation will develop. The bread will be more likely to absorb the water making it soggy, the paper absorbs some of the moisture protecting the quality of the product. The bread to foil contact can also become sticky and may tear the product apart as it is unwrapped. The paper backing also is more tear resistant when the product is being packaged into the foil.
