Collapsible containers save 60% space. made of silicone and FGP, BPA free. Ezysafe collapsible containers are suitable for the fridge, freezer, microwave and dishwasher (top shelf). The button on top is to release pressure when in the microwave or collapsing them. They are air and water tight as long as the button is in the down position. The collapsible contianers stack flat and come in 6 vibirant colours and 6 different sizes from 350ml up to 2L. Eazysafe collapsible containers are packed in a 4 set of the smaller sizes and a 2 set of the bigger sizes. You can save and by them together as a 6 set of collapsible containers also.