First, choose the substrate: pick MR for food contact, not MC.
The type of steel used for the tinplate determines its basic corrosion resistance. For food tins like for cookies or tea, MR steel is the top choice. Its residual elements are tightly controlled, giving it better corrosion resistance than MC steel, making it the standard for food cans and high-end gift boxes. MC steel has higher copper and nickel content, which makes its corrosion resistance a bit weaker, and it's mostly used for chemical containers, so it’s not recommended for food. Only when the contents are highly acidic (like tomato sauce) should you consider the most corrosion-resistant L steel.
Next, decide the tin coating thickness: #50 is enough for regular cookie tins, #75 for maritime export.
The tin coating is the first line of defense against rust and is measured in g/m². Cookie tins are usually stored in dry environments, and 2.8/2.8 (#25) is a bit low; 5.6/5.6 (#50) is the most common economic option, suitable for regular gift tins and tea cans. But if your tins are going for maritime export, facing high salt mist and temperature/humidity changes, it's recommended to upgrade to 8.4/8.4 (#75). This significantly improves rust protection, with only about an 18% cost increase, which is much better than having a whole shipment rejected for rust.
Finally, decide hardness: this determines if the box will get crushed.
Hardness (tempering grade) affects the tin's crush resistance and formability. Regular rectangular cookie tins usually go with T4 (medium hardness), which balances yield strength with structure and formability. If the box has deep embossing or rounded corners, softer T2/T3 is better for ductility, preventing cracking. Only for large gift boxes that need to be stackable should you consider T5/T6 hard grades.
One detail that’s easy to overlook: inner coating.
Cookies have a fair amount of oil, and direct contact with the tinplate walls for long periods can cause corrosion. The reliable approach is to request a food-grade inner coating (like epoxy-phenolic resin) to separate the contents from the metal. This isn’t the main choice of material, but without it, even the best material you selected earlier won’t matter.
