Do Stainless Steel Lunchboxes Keep Food Warm?

This is a question we get asked a lot. You have a delicious curry that you have just made or warmed up, you drop a couple of ladlefuls into your cherished Mintie Snug, perhaps with some rice the other side of the divider. And now you are wondering "Is this still going to be warm when I come to eat it?"

As with most things in life, there is a short answer (bad news), and a long answer (good news).

The short answer is "probably not" (the bad news). I am sorry, but stainless steel is a good conductor of heat, this means the heat from your curry is likely to find its way to the surface of the metal box and conducted to the next closet surface such as your bag or surface it is placed on. If you don't take special care, your nice warm curry will be tepid after an hour or so.

The long answer! (The good news) Well there are actually a number of things you can do to help keep your delicious meal nice and warm.

1) Place your lunch box in an insulated lunch bag! Just as insulated lunch bags help to keep you food cool in conjunction with some ice packs, they can help to keep hot meals hot! The insulation can be further improved by wrapping your lunchbox in a tea towel or cloth before placing in the bag. 

2) Warming your lunchbox first. This will help to increase the overall temperature of your meal + lunch box combination, improving its chance of being warm later in the day.

3) Give yourself a large portion! Yes, this is probable a win-win.. the larger the mass of warm curry, the longer it will take to cool down. Imagine if you just put a small spoonful on curry in a large lunchbox, it will obviously cool down quite quickly. Now fill that same lunchbox to the brim and it will take much much longer to cool down, all other things being equal.

4) Eat it sooner! Yes, this goes without saying that if you prepare your meal a little closer to the time you plan to eat it, it will more likely be warm. So maybe have your lunch a bit early.. it was always going to be hard to resist tucking into that currey anyway :)

Remember, it is the air that is the insulator. Even a cloth wrapped around your lunchbox will be a good insulator as it traps the warmth in little air pockets within the fabric. Insulated lunch bags are effective as they trap air inside them. If your metal bento box is placed on a metal worktop, it will conduct the heat very well through to the worktop. You can see this by the fact that the metal worktop will be warm after you have taken it away. If you place it on a wooden worktop, less heat will be lost through the base. 

do lunchboxes keep food warm hot until lunchtime?