I initially purchased the sippy cup version of these O-Sip! lids but now it’s time for an upgrade because we are teaching our son how to use a straw now. We find that these fit well on the plastic style theme cups that normally come with their own lid and straw only those aren’t spill proof and these are so we simply swapped out the lids. They do fit very nice and snug. You will have to place several fingers under them to stretch them out and slip them on. Be careful not to pinch your fingers in the process of slipping them out. Depending on the size of the cup the lids might be a little deflated or lumpy looking but not to worry it still won’t leak. These are really convenient both at home and when you are travelling too. I put one in our baby bag and we keep the other two in the kitchen.
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