What is the difference in the openings of the different teat sizes?
In an SS and S teat, the teat opening is a round hole. This means that if you hold the bottle upside down, milk will drip out without any sucking needed. This is perfect for young babies who have little jaw development yet as they don’t have to work too hard to get their milk.
In the M, L and LL teats, the opening is a crosscut. This means that if you hold the bottle upside down no milk will drip out, as the baby is required to suck on the teat in order to open the cross cut tip. This is perfect for babies as they get older and have stronger jaw muscles. A cross-cut also enables a baby to vary the flow of milk themselves – the harder they suck, the larger the cross-cut opens.