Do Insulated Lunch Bags Need To Be Refrigerated?

Insulated lunch bags are a great way to keep your food and drinks cold for a few hours, but you might be wondering whether they need to be refrigerated before you use them and if this helps them to keep your food cold for longer?

Insulated lunch bags slow the warming up of your food and drink with insulating foam and heat reflective materials. Putting them in the fridge before use doesn't help them to work much better however it is advise to keep them in the fridge with you food right until you leave to go to school or work as this will actively keep your food cold.

People leave their refrigerated bags into the fridge at work because this allows the fridge to actively keep the food cold. It doesn't actually help the lunch bag work better. A fridge will actually cool down your food while a lunch bag will just slow down the food from heating up quickly.

As soon as your insulated bag is taken out of the fridge outside heat will begin to seep into the bag slowly warming up your food. The insulation slows the transfer of heat but it doesn't stop it completely.

Keeping the lunch bag in the fridge before using it can increase its ability to keep the food colder to some extent as it'll cool down the foam insulation the lunch bag is made from. However, the impact of this on how long your food stays cold is negligible. The main impact comes from the fridge keeping the food inside the lunch bag cold right up until you take it out.

Less time out of the fridge means less time for the heat to warm up your food.

In this article we will look at how a lunch box actually works so you can decide when and when not to put it in the fridge.

Do Insulated Lunch Bags Need To Be Pre-Chilled In The Fridge?

Generally speaking, an insulated lunch bag doesn’t need to be refrigerated in order for it to work. Lunch bags are lined with insulated foam that slows down the heat from warming up the items inside. Refrigerating the lunch bag will actively cool the food down. However keeping it in the fridge isn't a requirement before using it.

When it comes to bulkier coolers they actually need to be pre-chilled before using them. High end coolers contain a layer of insulation that is 2-3 inches thick. This thick insulation can trap a lot of heat if left in a warm environment. 

This pre-chilling can really prolong the ice retention capacity of high-end coolers like Yeti.

However, there’s no need to pre-chill an insulated lunch bag. The insulation walls of a lunch bag are not thick enough to trap a significant amount of heat and so pre-chilling them has little to no positive effect on how long your items will stay cold for.

The reason you keep a lunch bag in the fridge before using it is to keep the items in the lunch bag cold right up until you leave, not to keep the insulation in the lunch bag itself cold.

The cooling effect of the fridge will also chill the walls and inside of the lunch bag so it will take longer for the internal temperature to drop down. 

Do Insulated Lunch Bags Need To Be Refrigerated To Work?

No, insulated lunch bags do not need to be refrigerated to work. The walls of a lunch bag are made of an insulating material like foam or a heat reflective material like aluminum. As these materials are good insulators of heat (they slow heat transfer) they can keep the food cold for a longer time than they would in a regular bag.

Heat is transferred through three different methods – conduction, convection and radiation.

Lunch bags minimize the heat escape by all three methods. The foam insulated walls slow down the transfer of heat through conduction and stop warm air getting in (convection).

There’s also a reflective layer inside the walls of a lunch bag that bounces back most of the heat that radiates from the food. 

There’s no material out there that can completely block the heat inside and as things go insulated lunch bags aren't that great at stopping heat transfer. Lunch bags only keep food cold for a few hours, but this can be extended with a good ice pack.

Vacuum insulation is the best at keeping things cold but most lunch bags don't have this type of insulation. Over time, the items inside the lunch bag eventually warm up but the insulation really slows down this process. 

That is the purpose of a lunch bag. It doesn’t make your food cold but only slows down how quickly the outside heat reaches inside.

The better the quality of your lunch bag the longer your food will stay cold. If you want your items to stay colder for longer then one of the best lunch bags is the Yeti DayTrip Lunch Bag. It's expensive but it has thick insulation and can keep items cold for up to a full day with the use of ice packs. Read my full Yeti DayTrip review or click the links below to see the latest prices.

Yeti DayTrip Lunch Bag

The Yeti DayTrip Lunch Bag is THE BEST lunch bag on the market (no question about it).

It's sized for personal food but features thick insulation that will keep ice for up to a full day. It expands to fit all your lunch and folds down to a super compact size for easy storage. An expensive lunch bag, but well worth it's price tag

See The Latest Price at See The Latest Price at Amazon

Benefits Of Putting Your Insulated Lunch Bag In The Fridge

Although it's not necessary to put a lunch bag in the fridge, there are still some benefits of doing so.

Refrigerating a lunch box increases the time your food stays cold inside because the cooling from the fridge brings down the food’s temperature and also chills the air inside the lunch bag.

Keeping your lunch bag in the fridge will keep the items from warming up at all. As long as the lunch bag stays inside the fridge the items inside will be maintained at the fridge’s temperature.

You can achieve a similar result by putting ice packs in your lunch bag but if they aren't keep in the fridge things will eventually warm up to room temperature.

Putting your insulated lunch bag in the fridge also helps you keep the food together. All your food items can be easily organized in the lunch bag and you can take them out whenever you need them. It will save you a lot of time.

Can You Put An Insulated Lunch Bag In The Fridge? Is It Safe?

Putting an insulated lunch bag in the fridge won’t cause any damage to the lunch bag. The fridge only lowers the temperature of items by using cold air so there’s nothing to be worried about. 

Most lunch bags are made from sturdy material and can easily survive harsh temperatures.

You will only damage your insulated lunch bag if you keep water or ice cubes in it. The water can seep into the walls of the lunch bag. 

This water will get trapped inside causing mold to grow between the walls. That’s why it is advised not to keep loose ice inside the lunch bag

Can You Put Insulated Lunch Bags In The Freezer?

Yes, you can definitely put an insulated lunch bag in the freezer. Keeping a lunch bag in the freezer won’t damage it. It will still cool down the temperature of your food inside the lunch bag. If you want to keep your food frozen inside your lunch bag then you should absolutely leave it in the freezer right up until you need to take it with you.

However, because the lunch bag is covered it’s difficult for the chilled air to get inside freely. So the items will still cool down but at a slower rate as compared to if they were kept in the freezer without a lunch bag.

Some lunch bags are specially designed to be kept in the freezer prior to use. They contain ice packs between their walls that need to be completely frozen to cool down the items inside. 


There’s no need to refrigerate a lunch bag in order for it to work. 

  • Lunch bags are lined with insulating material that minimizes the exchange of heat between the inside and outside through convection and conduction. There’s also a shiny layer that prevents the transfer of heat through radiation.
  • Refrigerating a lunch bag does help as it actually chills the items and air inside so it will take longer for the temperature to lower down.
  • There’s no need to pre-chill an insulated lunch bag like coolers.
  • Keeping the insulated lunch bag in the fridge or freezer won’t cause any damage to it. 
  • Refrigerating an insulated lunch bag will prevent the items from warming up at all and also help to keep things together. 
  • Use ice packs in your lunch bag once you take it out of the fridge to help keep everything cold. Learn how to make DIY ice packs for your lunch bag.