No more mystery blue goo. This ice pack is the same size as a small iPhone, made from 18/8 stainless steel and filled with distilled water. It fits perfectly in Onyx sandwich boxes, as well as in many other sandwich boxes and food containers. Slip directly into the food container as it can go directly against the food. Going to a potluck? Place one in the bottom of the bowl for potato/egg/pasta salads to help keep things cold. It is also great for putting on bruises, headaches, sore backs etc. Plastic and BPA-free, freezes quickly, and made from sturdy stainless steel - so they will last plus it is 100% recyclable.