In chemistry, the term inert is used to describe something that is not chemically active, i.e. a substance that does not react with other substances or break down over time. 

Similarly, the concept of inertness in food contact materials describes a material’s potential to react and exchange chemicals or compounds with the food or beverage it is in contact with. 

Examples of non-inert materials that react with foods can include plastics or paper & board. While materials like stainless steel, glass, and glazed ceramics are highly inert and have little reaction with foods.

When food is in contact with a non-inert material, chemicals may leach into the food and vice versa. You might have observed this phenomenon before when a plastic container is stained red after storing tomato sauce in it. Not only did parts of the tomato sauce enter the container, but parts of the container also leached into the tomato sauce. This effect is especially strong for hot, fatty, and acidic foods. 

Using more inert materials helps to reduce potentially harmful chemicals from leaching out of food packaging and other food contact articles into food.