I used to use airlocks but just recently tried foil because of flyangler's thread. It seemed to work OK (it went like any other starter though...no different) but I still was uneasy about having a 'finished' starter just sitting there with no airlock. Once it's finished it doesn't really have much positive pressure. I'm still unsure of the improvement of foil over an airlock when you're not using a stirplate (I'll get/make a stirplate someday but I don't have one now). It just didn't seem to go any different than using an airlock.