It's what backpackers used to use.
It's mentioned in this Wikipedia stub.
And here's a very nice summation, nicer than I could manage on short notice.
I'd go with the foam, 'cause I remember doing two layers of moleskin in order to properly protect a blister. The foot section of Walgreen's will have it. Or your friendly, neighborhood camping store/REI.
Oh look, REI has a blister section.
It may not be what you're looking for, but there is something to be said for checking out the old tried and true methods.