I have a son and the first thing that interested me when I bought  Doctor Browns  free is that this  bottle helps prevent  colics.  The bottle comes with 3 separate parts the bottle itself and there are two plastic small parts that you put inside the bottle before you screw in the nipple.  Those are the parts that are supposed to prevent colics because they control  the amount of air that gets through when the baby is using the bottle.  It is a good quality product and I would recommend it. The only thing that I did not like about it was those small parts that you have to assemble before...