They are made from #316 (18/10) food grade Stainless Steel, (The best of the best!) and the lid has a silicone seal. The containers are completely air tight.
You can also write on the container with a non-permanent marker. This helps to specify the contents, date and owner. The bottom part of the container can be washed in the dishwasher, but the lid is not dishwasher or oven safe. Made in Korea.