It's the plastic package that covers the bottle opening completely. The
airtight seal is made by the threads of the screw ring that contains the
nipple. The air that passes thru the nipple hole meets only with the top
surface of the plastic package. It's like covering the bottle with plastic
wrap & screwing down the cap to assure that air doesn't pass thru the screw
threads.
>
> But the nipple has an opening in it doesn't it? So this isn't really air
> tight...??
> Cindy
> >>
> >> We take the plastic package from the nipple, place the sterile side
over
> >> the opening to bottle & cap it with the nipple to make it air tight.
> >>

--- Phyllis Adamson, IBCLC
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