If you're taking a bag lunch to work or school or you’re planning a trip and want to bring some snacks with you and want to keep them cold then insulated lunch bags are a great option.
But how long will your insulated lunch bag keep your food cool and safe without them?
Insulated lunch bags don’t require ice packs, but your food will stay colder much longer with ice packs. Insulated lunch bags only slow down how quickly your food gets warm, they don't actively cool food and without ice packs food warms up quickly. If you need to keep things cold longer than 1-2 hours, you should include an ice pack in your insulated lunch box.
If you’re taking your lunch box to work and plan on sticking it in the fridge when you get there, then an ice pack might not be necessary as food won't warm up enough of your commute to be of any concern.
But what about for longer periods of time?
Let's take a closer look at how insulated lunch bags work, whether you need to include and ice pack or not and why you likely want to consider an ice pack for longer trips.
How Do Insulated Lunch Bags Keep Food Cold?
Insulated lunch bags contain a foam layer that keeps your food cold by keeping outside heat from reaching it. The foam layer contains many tiny pockets of air and it's actually the air that stops heat transfer, keeping the food inside your insulated bag cold and stopping the outside heat getting in.
Many insulated lunch bags also have a reflective lining made of foil that’s heat reflective. This reflective foil reflects heat radiation (which foam doesn't protect against) keeping the food inside cooler for longer than a bag without the reflective layer.
The combination of foam + reflective layer is what helps keep items inside an insulated bag cold for longer.
Some cheaper and disposable insulated bags use plastic or paper/cardboard instead of foam but they work in the same way. The plastic or paper insulates against heat and the foil layer reflects heat radiation. The thicker the plastic, paper or foam the better a bag is at insulating.
The Yeti DayTrip Lunch Bag (shown above) is arguably THE BEST insulated bag and can keep ice frozen for over a day.
It's important to note that insulated lunch bags do not actively keep food cold. They just slow the warming process. Ice packs are usually added to actively keep food cold as they absorb heat from your food.
Your lunch bag may be able to stay cooler if you’ve put it in a refrigerator before packing it.
The temperature of the food you put in your insulated lunch bag also matters. If you’re packing cold drinks and food, the inner lining will reflect the cooler temperature and keep your food cooler for longer.
Do Insulated Lunch Bags Actively Keep Food Cold (Without Ice Packs)?
Without an ice pack, insulated lunch bags don’t actively keep your food cold.
Instead, they slow down how quickly heat can reach and warm your food, and if I'm completely honest they do an ok job at this but not a really great job.
While a cooler can keep things cold for days at a time an insulated lunch bag can keep things cold for a few hours (maybe 6-9 hours maximum).
The foam lining is the most essential part of how slowly your food heats up. The thicker the foam insulation is, the longer your food will stay cool.
Insulated lunch bags are usually made with soft, thin, open cell foam which isn't as effective at stopping heat transfer compared to the closed cell foam of something like a Yeti cooler.
This mean that while an insulated lunch bag will slow how fast your food warms up, without an ice pack that food will likely warm up in a matter of 1-3 hours on hot days and maybe slightly longer in colder temperatures.
Your lunch bag doesn’t cool your food so you use ice packs to do this. Because ice packs are likely colder than the food in your lunch bag heat is transferred from your food into the ice pack – keeping your food colder for longer.
It’s essential to remember recommended food safety guidelines and keep your food within recommended temperatures! Once your food becomes too warm bacteria can begin to grow faster and this can spoil your food.
Where you put ice packs in your insulated bag plays a role in how cold food will stay and how long it will stay cold for and they type of ice pack you use also plays a role in this. See my recommendations for the best ice packs for lunch boxes and coolers.
Insulated Lunch Bags Will Keep Food Cold Without Ice Packs, But Not For As Long
Insulated lunch bags WILL keep food cold longer than if you don't use an insulated bag. However, your food will warm up fairly quickly if your insulated lunch bag doesn’t have an ice pack.
Depending on the quality of the lunch bag, you should make sure that you’re going to eat your food relatively soon or plan to put your lunch bag in a refrigerator.
Even in high quality lunch bags like the Yeti DayTrip food will warm up extremely quickly if there is no ice pack in there
Cold foods need to remain at 40℉/4ºC or below to keep them safe for extended periods of time.
Without an ice pack, an insulated lunch bag will only be able to maintain that safe temperature for a few hours. A gel ice pack can extend that time by 3-4 hours and a large ice pack or frozen bottle of water even longer.
Read more about how long gel ice packs last to make the most of your trip.If you don’t have a way to keep your food cool, then you can’t rely on your insulated lunch bag to keep your food safe for a whole day.
How Long Will An Insulated Lunch Bag Keep Food Cold Without An Ice Pack?
Several factors impact how long your insulated lunch bag will keep your food cold without the use of an ice pack:
- The type of bag you’re using
- The outside temperature
- The contents of your lunch bag
A general rule is that your insulated lunch bag will keep your food cold for about 1-2 hours without an ice pack and it'll likely be safe to eat for 3-4 hours after packing it.
If you’ve packed cold or frozen drinks or food, that time extends to 4-5 hours.
Any longer than that and your food will warm up and you’ll risk your food reaching unsafe temperatures that could make you sick. This is especially true for milk products.
How To Keep Food Cold In Your Lunch Bag Without An Ice Pack
If you don’t have an ice pack handy, there are many ways to keep your food cold in your insulated lunch bag.
- Don’t mix food temperatures. If you want to keep food cold, only put cold food in your bag. For example, don’t mix a cold water bottle and a warm container of pasta!
- Make your food cold before putting it in your lunch bag. Refrigerate your sandwich or leftovers, and refrigerate or freeze your drinks. Having food that’s cooler initially will slow the warming process.
- Keep your lunch bag out of the sun. If your lunchbox is in direct heat, it will warm up more quickly. Keep it in the shade if possible.
- Store it in the fridge. This tip might seem like a no-brainer, but putting your insulated lunch box in the refrigerator as soon as possible helps keep the food inside safe.
- Use insulated food containers in your bag. Insulated containers will also add an extra layer of protection by keeping whatever’s inside of them at the right temperature for longer! You can also wrap your whole lunch bag in a towel for extra insulation.
- Minimize empty air space. This might seem odd, but keeping open air to a minimum will help keep your food cool. If the air can’t circulate much, it can’t warm up!
What Can I Use Instead Of Ice Packs In My Lunch Bag?
If you’re crafty, you could make your own gel ice pack with things you probably already have in your house!
Another great option is to freeze a water bottle or two and throw it in your lunch bag. A cold or frozen water bottle will work similarly to an ice pack and help keep your food cooler for longer. It also has the added benefit that as the water bottle melts you can drink the water – refreshing you and cutting down on weight at the same time.
You could also freeze your food, and it will slowly thaw in your bag but still be safe by the time you take it out to eat. The denser the food the longer it'll take to thaw out.
We don’t recommend using loose ice in your insulated lunch bag. If your lunchbox is cheap, it probably isn't waterproof, and as the ice melts, it could get into your food. There are some waterproof soft coolers that can double as lunch bags but these are usually pretty large and wouldn't fit in a backpack but are separate bags you can take with you.
Insulated lunch bags don’t need ice packs if:
- You’re planning on eating the food inside within 1-2 hours.
- You have an alternative, like a frozen water bottle, to keep food cold.
- You can put your lunch bag in the refrigerator within an hour or two.
Otherwise, you’ll want to use an ice pack in your insulated lunch bag to keep your food cool.