Once you get used to the tightening the lid (briefly turn in the opposite direction until it "clicks") are the cup with us constantly in use. They are stackable, easy to clean and I order just to complement the larger cup (240ml) - if I still need more milk portions soon. Especially great are the 2 adapter so I can save the washing up elaborate use of an extra baby bottles by giving the cleaner directly onto the adapter after warming up. I'm very satisfied and regret so far as buying an extra once-milk bags of plastic - I've never used again for the cup in the household.