The Avent bottle is the only bottle that uses the unique Avent silicone nipple with the patented anti-vacuum air valve. The dome cap seals the nipple for spill-proof mixing and transporting. Made of dense durable polycarbonate plasic these bottles hold up in the dishwasher and are boilable and microwave safe. The Avent silicone nipple is broad and soft with a natural shape. This allows baby to suckle like when breastfeeding unlike most other standard bottles which limit baby to a sucking motion. And because the Avent nipple so closely mimics the form and function of the breast babies will be able to alternate easily between breast and bottle feeding helping mom to breastfeed longer. Both the Avent reusable and disposable nipples feature an anti-collapse tip and are available with several different flow rates to accomodate baby's changing needs. Laser cut holes precisely regulate the rate of flow and do not change in size over time. Nipples that are included with the bottles are t