Already the small cup gifted as a set and again ordered the major to me. Have used it both as a container for expressed milk and with the same attachment as bottle, for others I keep there the milk substitutes on. If one ensures that the lid closes properly, the containers are leakproof. They can be stacked and later there freezing and warm homemade porridge. They fit well into the Avent bottle warmer. Accordingly, they do what they should.