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? 
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.  