If you own a stainless steel lunch box, chances are, it's 100% stainless steel and nothing else. They are the ultimate in eco-friendly and they can be recycled if you ever decide you don't want it anymore or you bend it so far out of shape it's beyond repair, but the one small issue that people can have with lunch boxes like this is that over time, the lids can become a little loose. Whether it's the Lunchbots brand that we have here at Shop Naturally or any other brand, the issue isn't tied to one brand, it's tied to the design of a stainless steel box and a stainless steel lid firmly sliding over each other with no clips or silicone seals or plastic to hold them in place.
We have road tested many brands in our time, and most of them didn't pass our quality control. Cheaper lunch boxes can have rough edges, warped lids, lids that don't go on properly or stay on properly and a dull surface with scratches all over it. In the Lunchbots factory, each bento lunch box they produce has the lid fitted to that box with the goal of making it easy enough for a young child to open it, so if you have more than one, it's important that you don't swap lids around or you could have some small fitting issues. Their new Lunchbots Clicks fixes all this with a clip down lid and silicone seal, but the regular rectangular bentos can have their lids loosen over time.
You can perform a simple adjustment to any stainless steel lunch box with a stainless steel lid if they become loose. This needs to be done by an adult. With both hands, pull out on the long sides of the container in a quick motion with moderate force. After this, d the same thing on the two short sides of the lunch box. Test the lid and see if it's any firmer. You can repeat this action if you think it needs a little more.
With a much gentler motion, you can also try the opposite on the lid, with a gentle pushing in of the long sides and then the short sides. Remember, stainless steel does bend, so over time, they can be bento out of shape with repeated use.
If your issue still persists, ensure you're always placing your stainless steel lunch box snugly packed inside your insulated lunch bag so there is no rattle room for the lid to come off. If there's room in your bag, pop a small drink bottle on the top to hold it in place, or an ice pack, a juice box, a snack, or something that will get used during the day to fill up the bag. Alternatively, a wide piece of elastic from Spotlight or the sewing section of any supermarket / department store will hold the lid firmly in place.
Remember, stainless steel on stainless steel does always mean that your lunch box is NOT leakproof. If you're trying to store any liquids or salads with dressings, regardless of how well the lid fits, you will get some leakage. Try the new Lunchbots Clicks for a leakproof solution.