Where do I begin with these? If you're thinking about using them as a substitute for the Drop-Ins...please don't. They don't fit well in the Playtex Drop-Ins nurser bottles. I ended up using a Drop-In liner underneath these in order to use these, because these alone will leak...a lot. The thickness of the Drop-In liner is needed in order to make a seal that won't leak. These liners are a pain to put into the bottle. They need to be added in very carefully, which isn't good at all when you're on the go or in a hurry...and especially not in the middle of the night. There's plastic tabs you need to tear off before giving the bottle to your baby, and the perforations on the tabs make them hard to tear off. These are pretty useless also if you make one bottle at a time and shake it. You'll need to either use breastmilk or formula prepared in another container. These liners make preparing your baby's bottle so much more hassle than it needs to be and in my opinion are a waste of money.