These have got to be the best bottles I have ever used. Playtex ventaire bottles are designed to help baby by reducing gas, colic and spitting up.
The first time I had ever used these was with my first daughter 3 yrs ago, with my second I changed to another brand of bottles, which I didn't like in the least, with my son whom is 9 months old I am again using the Ventaire bottles, I haven't found another type to beat these.
The bottom is full of holes which is then coved by a silicone insert, that easily screws on the the bottle, the nipples comes in stage one for newborns and stage two for older babies. The neck on the bottle is angled slightly to help baby drink in a more upright position, the holes on the bottom ring is what helps with the gas, colic and spitting up.
These bottles are the easiest bottles I have ever cleaned, they can be put in the dishwasher, I prefer not to do that, I always clean my bottles by hand with a bottle brush, I simply remove the bottom ring and the brush slides right through getting every part of the bottle then I just wash the top and bottom ring, the silicon insert and nipple. Let them dry and screw them all back together.
I highly recommend these bottles, they are great and I have never had a problem with my babies having gas, colic or excess spitting up.