i figured out the mystery of the collapsing Born Free nipples!!!
i was getting so frustrated. DS is 2.5 months old and i just started using level 2 nipples because he was always collapsing the level 1s (and he was eating waaaayyyy too slowly) and the level 2s were collapsing!
so i called born free. she said my venting systems were closed. she said when you wash them, they close. all you have to do is pinch the "nipple" part of the venting system (the part that sort of snaps onto the bottle) so that you see the slit open up. that's it!
so i tried it....and she was right! no more collapsing nipples!!!
(she also said not to over tighten the tops...but we LIF ladies know that already!)