These bottles are so frustrating! They leak all over the place and a friend said that you have to make sure they're completely dry before tightening. Who designs a bottle specifically made for liquid that must be dry to prevent leakage? It's so frustrating to see the breastmilk that you worked so hard to pump flying all over your kitchen as you shake it up. I've thrown my Avent bottles away and will not recommend them to anyone who values their expressed breastmilk (or expensive formula!).