The Ultra Seal 5.7 Cup Square food storage container features a blue color-coded matching system to help find and watertight seal that keeps food fresh and prevents liquids from leaking. A vent in the lid releases steam when the container is placed in the microwave, and all containers store efficiently both when in use and when not in use. UltraSeal containers are freezer, microwave and dishwasher safe, as well as BPA-free and phthalate-free.a-seal locking contol.