In particular it is used to feed an infant with infant formula, expressed breast milk or pediatric electrolyte solution.

Dimensions and design

A large-sized bottle typically holds 270 ml; the small size 150 ml. It is composed of a bottle itself, a teat, a ring to seal the teat to the bottle, a cap to cover the teat and optionally a disposable liner.

The height-to-width ratio of bottles is high (relative to adult cups) because it is needed to ensure the contents flood the teat when used at normal angles; otherwise the baby will drink air. However, if the bottle is too tall, it easily tips. There are asymmetric bottles that ensure the contents flood the teat if the bottle is held at a certain direction.

Teats (or nipples)

The teat itself is typically slimmer and more flexible than the mother's nipple. Contents of a bottle can flow more quickly than breastfeeding. Specialized teats that attempt to mimic the shape of the breast exist to help babies to switch back and forth between bottle feeding and breast feeding for cases where "teat confusion" occurs. Teats come in a selection of flow rates. Different flow rate teats either have more holes or larger holes. The correct flow rate needs to selected based on the age of the infant. Variable flow rate teats are available for older infants. The hole is asymmetric so that by turning the bottle/teat, different flows can occur. Specialized teats are available for infants with cleft palate (see also Haberman feed).

Vented bottles

"Vented" bottles allow air to enter the bottle while the baby is drinking without the need to break the baby's suction during feeding. Alternatively a bottle liner can be used to enclose the formula instead of directly in the bottle. The liner collapses as the formula is drained.

Vented bottles work by allowing air to enter while preventing the liquid inside from escaping. Avent is the most popular brand in this category. It works by an "anti-vacuum skirt" in the base of the teat, where it forms a seal with the bottle. The skirt acts as a one way valve, allowing air to enter the bottle but not liquids to leave. If the sealing ring is tightened too much, the skirt is compressed too tightly to allow it to open and the bottle will not vent. If the sealing ring is too loose, liquid leaks from the bottle.

There are multiple patents for technologies in this area. Initial designs called for a complex spring and valve system that was impossible to clean and sterilize. Current research is in specialized materials with microscopic pores that allow the entry of air without the escape of liquids. This avoids the caregiver having to get the sealing ring tension just right. It remains to be seen whether these materials can withstand the rigours of daily cleaning and sterilization. Another competitor, Dr. Brown's, offers a system whereby the vented air is conducted through a tube to the bottom of the bottle where the airspace is when the bottle is in use. This avoids the vented air from bubbling through the liquid and unnecessarily aerating the liquid.