Anyone know why teat size 2 is collapsing all time?

[CantThinkOfAGoodUserName]

DD is 7 months and was on size 1 until recently as they suited her but then she kept getting bored before finishing bottles so I switched to next size up and she's happy but it keeps collapsing in... What's that all about? It's tommee tippee bottles and teats

Is it the ones with the little vent in the teat? Sometimes you need to squeeze the vent open otherwise it collapses

Good call! I remember those vent thingys on size 1, went to check and there isn't a vent thing!
Says anti c

Anti colic on it though ??