Hmmm .. for potatoes I don't like to use foil. Best, crunchiest skinned potatoes are done like this;
- Scrub them
- lots of fork pokes
- rubbed with olive oil
- add kosher salt to the skins
- bake directly on oven rack (unwrapped) for about 90 minutes (depending on how many you're baking)
- should add foil to the bottom to catch the oil drippings
Best potato, hands down.