The straw on our new style sippy cup has a pressure valve (this is the magical piece that makes it leak-proof).
Bubs need to place their lips over the whole straw (rather than just the tip) and press down on the straw, to open the valve and enable liquid to flow.
This new design means the sippy cup can be used with both warm and cool liquids.
All littlies are different – some adjust to the straw straight away and others need a bit more time.
Encourage them to explore and they will get there!