Can anyone help me find this thing my grandmother was telling me about to reduce wind in babies

[Lollibert]

she used it for her babies you could buy it from a chemist they were these special bags that go inside the bottles to reduce wind she said you’d put the bag inside the bottle then put the milk in and then screw on the teat and it would reduce air

I haven't seen exactly that before, but mam bottles have something similar, a rubbery thing in the bottle that lets air in

Not what you are after but I swear by Dentinox

Oh you won't get those any more my mum recommended them to me 30 years ago and they didn't exist then ! DR brown bottles have a thing in them that does the same thing.