These bottles are a MUST! They are VERY inexpensive, yet have cute designs and work so wonderfully! They have airflow holes at the bottom, paired with a specially shaped nipple that helps prevent baby from getting tons of air in their tummys. It prevents gas & spit up because of no air getting to their belly. The BEST part is that the bottom unscrews & so does the top, so the bottle comes completely apart to EASILY wash & sterilize! I was shocked how inexpensive they were for how amazing they were. I would even purchase if they were mor expensive because of how well they work. My daughter had major acid reflux & these were recommended by her pediatrician, we got them and they worked wonders! She was able to stop her daily prescription medication! Her episodes of acid reflux were so bad that she would stop breathing for a second & those episodes stopped when we got these bottles!