Q: Which way does the foil face (reflective side) on the AP foil faced insulation need to face?
A: In most cases it doesn't matter. Both sides have the same perm rating (0.05 perms). The reflective side will give an increased R-value when used behind an exterior brick veneer. This is called a reflective air space. Sometimes the non-reflective side is installed towards the outside to reduce glare from the sun or to eliminate any concerns about too much heat build up behind vinyl siding.