As close to breastfeeding as possible. Medically researched to mimic the peristaltic (wave-like) motion of sucking during breastfeeding so nipple confusion can be avoided when combining breast with bottle feeding. Includes 1 x (SS) sized teat for babies 0 Months + Teat is the perfect shape and size to fit into sucking fossa of baby Inner vertical lines strengthen the structure; making it collapse resistant Textured surface allows baby to latch on easily and securely 100% Silicone nipple; super soft and flexible, allows natural and smooth tongue movement. Air Ventilation System (AVS) reduces intake of gas, a potential cause of colic. 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.