These are hands down the best design for anti colic bottles, they are vented and allow air in, that being said if you fill a bottle and attempt to travel with it it will leak, unless you remove the nipple ring, vent and cap and use the solid caps or disc with the nipple rings. If you overfill the bottle the venting system fills with formula, if enough formula gets into the vent tube it will leak, that liner that say do not fill above line, it means it, the closer you are to the capacity of the bottle the higher the likely hood of this happening. If you lie you child back while feeding the risk diminishes the more upright and level the bottle the higher the likely hood. The original natural flow vent cap is more resistant to issues in my experience. The tube goes ... MoreThese are hands down the best design for anti colic bottles, they are vented and allow air in, that being said if you fill a bottle and attempt to travel with it it will leak, unless you remove the nipple ring, vent and cap and use the solid caps or disc with the nipple rings. If you overfill the bottle the venting system fills with formula, if enough formula gets into the vent tube it will leak, that liner that say do not fill above line, it means it, the closer you are to the capacity of the bottle the higher the likely hood of this happening. If you lie you child back while feeding the risk diminishes the more upright and level the bottle the higher the likely hood. The original natural flow vent cap is more resistant to issues in my experience. The tube goes over the the vent cap, while on the the options plus the tube fits into the vent cap. the latter if not seated all the way in or tilted will allow milk/formula to enter the segregated chamber and if it fills enough then it will leak. These are Great Bottles and they are complex and simple at the same time. I love them but i dread cleaning them, we have twins and I spend about 1 to 1 1/2 hours daily washing ans sterilizing bottles every day. A little patience and making sure the components are assembled correctly and they work flawlessly. My biggest complaint is available replacement parts. I need caps, and can not find the ones without buying a vent tube and other accessories. Plus my OCD wants to match the original colors of my bottles and not have mismatch components.

I have used these bottles while babysitting. They worked fine then. Now after having my baby, I was gifted these and would have totally recommended these to anyone.Needless to say, I am horribly disappointed in these bottles both anti colic and natural flow. These bottles are leaky, some persons recommend not sterilizing with boiling water, but only with a steamer. Dr Brown needs to clarify this for all time sake. Formula is wasting and the mess is a frustrating disaster.Added to that, I cannot say that they prevent gas or colic in anyway because since using this product my baby is really gassy and has plenty gas.Overall I think we all deserve an explanation or a refund or an apology. It's not just the product. It's that the company is unapologetically ... MoreI have used these bottles while babysitting. They worked fine then. Now after having my baby, I was gifted these and would have totally recommended these to anyone.Needless to say, I am horribly disappointed in these bottles both anti colic and natural flow. These bottles are leaky, some persons recommend not sterilizing with boiling water, but only with a steamer. Dr Brown needs to clarify this for all time sake. Formula is wasting and the mess is a frustrating disaster.Added to that, I cannot say that they prevent gas or colic in anyway because since using this product my baby is really gassy and has plenty gas.Overall I think we all deserve an explanation or a refund or an apology. It's not just the product. It's that the company is unapologetically standing by their product and either ignoring the reviews or being proud.Sad to say, I would rather invest in a drugstore, unbranded bottle just to know that I got my money's worth and little expectation

I absolutely love these bottles. I’ve noticed a significant difference between THESE particular ones, and the other ones. One of those differences just so happens to be leaks! Before I proceed, I’m just going to call the bottles as I see them as I do not know the terminology for them. Now, the bottles with the blue ventilation system appear to be the same as the bottles with the green ventilation system, and I made that assumption as well. And then the leaking started with the bottles that had the blue ventilation system. I tried everything. Using the ventilation, not using it, nothing worked. I then realized the bottle caps that held the nipples were different. They were shaped differently, seemed more secure, and most importantly didn’t leak. I experimented the ... MoreI absolutely love these bottles. I’ve noticed a significant difference between THESE particular ones, and the other ones. One of those differences just so happens to be leaks! Before I proceed, I’m just going to call the bottles as I see them as I do not know the terminology for them. Now, the bottles with the blue ventilation system appear to be the same as the bottles with the green ventilation system, and I made that assumption as well. And then the leaking started with the bottles that had the blue ventilation system. I tried everything. Using the ventilation, not using it, nothing worked. I then realized the bottle caps that held the nipples were different. They were shaped differently, seemed more secure, and most importantly didn’t leak. I experimented the blue ventilation inside of these bottles and they worked wonders so my BUT from earlier is WHERE CAN I BUY JUST THE TOPS? No, not a bottle cap cover, not something for storage, THESE particular tops because that is all I need