A thermos is a terrific container to have on hand for sending a hot thermos lunch to school, and while manufacturers advertise how long their brand keeps food hot, the length of time will vary by brand and how you send it to school.
If you want to keep food hot in a thermos and have wondered how long it stays hot and how to pack hot and cold in the same lunch bag, this post explains it all and includes a comparison chart of top containers by brand.
How long does a thermos keep food hot
The amount of time you need to keep food hot will depend on the time you pack the lunch and heat the food and the time it will be consumed. On average, most of us need to keep food hot anywhere between 6 and 7 hours.
Depending on the brand of thermos lunch container you purchase, food will stay hot for between 5 and 12 hours! Yes, there’s that big a difference!
Check out this comparison chart by brand and price:
|Brand||Hours Hot||Price (avg)|
|Thermos Foogo||up to 5||$15|
|Thermos Funtainer||up to 5||$15|
|Lunchbots||up to 5||$34|
|Stanley (Heritage)||up to 8||$24|
|Stanley (Legendary)||up to 12||$24|
|Mira||up to 5||$16|
|Omiebox (all-in-one)||up to 4||$45|
You’ll find a full comparison of each of those thermos lunch box containers and their features in this post.
You’ll also find these thermoses and other favorite lunch containers inside this school lunch supplies page on Amazon here.
How to keep food hot in a thermos for Lunch
The best way to get the most out of your thermos container and the longest time possible to keep the food hot inside is to ensure that you’re using the thermos property.
In other words, to keep food hot in a thermos, it’s best to heat the food to the right temperature, preheat the thermos, seal it correctly, and pack it inside an insulated lunch bag so cold outside temperatures don’t bring the temperature of the food down from the outside in.
Read more on using a thermos the right way and how to heat it up here.
Is it safe to keep food warm in a thermos?
Food that was properly cooked and then heated up correctly before being placed inside the thermos will be safe to eat for hours after being packed inside the thermos container.
This is where deciding on the best thermos container for your needs will come in handy since the length of time it’s kept hot varies by brand (as shown in the chart above).
How to Pack Hot and Cold Lunch Together
Packing hot and cold lunch foods inside the same lunch bag is possible by placing the hot food inside a thermos and the cold items, such as fruits and veggies, in a separate single compartmentalized container or inside multiple lunch containers.
What is not recommended is to place an ice pack inside the bag since that will cool down the temperature inside the thermos container from the outside in. Here is a quick video showing you how to pack hot and cold lunches the right way:
Best Hot Food Thermoses
There are a few things to consider when deciding on the best hot food thermos container that fits your needs. Below are the top 4 we’ve tested, and thousands of families have loved for years.
Holds 14oz (1 ¾ cups) of food, stays hot for up to 8 hours, is dishwasher safe, and has a lifetime warranty.
Holds 10oz (1 ½cups) of food, stays hot for up to 5 hours, is dishwasher safe, and the rubberized lid makes it easy to open which is perfect for younger kids.
Lunchbots Food Jar
Holds 16oz (2 cups) of food, stays hot for up to 6 hours, is dishwasher safe, and a container that can grow with the child for years to come.
You can’t go wrong with any of the options above for packing lunches. A thermos is a terrific vessel for repurposing leftovers and sending hot and cold foods for lunch!
If you need ideas to fill the thermos containers, check out our meal plans. Our real food dinners can yield leftovers, and our lunches will add variety to any lunchbox, guaranteed.
Plus, you get a shopping list, a meal-prep sheet with a breakdown of what to prep when… it’s practically a kitchen assistant at pennies per day. Want to try it out first before you commit? Get a free week of our meal plans here!
One thing to consider prior to sending food in a thermos for the first time is to let your child try it at home first, so they are comfortable opening and closing the container own their own. A great place to start is with these delicious thermos soup recipes.
What are some of your favorite things to pack inside a thermos?
Very good information found here. I live in Georgia and Florida most of the year. Outdoor activities are super popular and we, husband and I, regularly pack our thermal jars for trips kayaking, boating, fishing, site seeing, etc. That said, we also take a backpacking Canister-style stove with us to reheat foods we’ve packed. Our tip is this: pack foods such as cooked Spaghetti, cooked Meatloaf, cooked Stuffed Green Peppers, in a thermal jar the night before. Place the jar with the food contents in the freezer (important: lid must be off) and leave it to freeze overnight until rock hard solid. Next morning put the lid on it and enjoy your day. By dinnertime the food is thawed enough to take out of the thermal jar and heat for your meal. Excellent to do this for wild camping!
This article is too informative. I really recommend to my friends and family.
Thank you!!! Appreciate your thorough information!!
Not a mom, but thank you! This was a very helpful thing for me to read since I recently learned about food “danger zones” (I admit I’ve been living in a hole). All the other reviews would just say things like “cold”, “warm”, and “hot” but you actually gave the temperatures which is what I needed!
MOMables - Laura
That’s exactly why I wrote that post! Glad you found it helpful.
I’m new at packing school lunches and I was wondering if packing a thermos filled with hot food in a lunch bag that contains ice pack and cold snack impact the temperature of the food in the thermos?
MOMables - Laura
Hi Azucena! This video is exactly what you are looking for to show you how to pack hot and cold foods in the same bag. Enjoy!
I had the same question. Which video shows how to pack a hot thermos with an ice pack?
MOMables - Laura
Lyndsy, check out this video.
No it does not affect the temperature in a thermos by any noticeable amount because the vacuum in the thermos walls prevents a fast transfer of hot and cold inside or outside. That’s why the food stays hot or cold.
Hi, I’m just wondering how exactly you preheat the thermos? (I’m specifically looking into the Stanley one)
They all really work the same. Here is a link to an older post: https://www.momables.com/how-to-warm-a-thermos/
Helpful article. thank you.
Would you know if when I put during lunch time a hot soup into a Thermos container (double wall stainless steel) and keep it there until the next day and reheat it in microwave, if it is safe to eat for an adult? It is a vegetable soup.
This would not be safe. Stainless steel cannot be heated in a microwave.
Thank you for this post! Your comparison of various products is very useful! I am specifically looking for an insulated container which does not have any plastic touching the food. The Lunchbots fits the bill, but the lid is a bit wide for my 4 old. Have you come across any other newer ones which don’t have plastic on the inside of the lid?
Also, could you please share which is the drinks container you use in the video?
I have not found any thermoses that do not have plastic on the lid. sorry! Here are our top lunch containers: https://www.momables.com/top-5-lunch-containers-for-school-office/ and our essentials: https://www.momables.com/back-school-lunch-essentials/
and here are the thermoses: https://www.momables.com/top-5-thermos-containers-for-school-lunches/ I Hope this helps!
Is it safe to keep baby soup for 8 hours in Thermos?
I take my baby to the office, and she needs to eat lunch at 12pm and “dinner” at 4pm. We leave home at 8am
She doesn’t like instant baby food and jar food :(
Thank you for this post – it had just the answers I was looking for!!
I know this posting is quite old, but I was curious to see if you had mold issues with any of your thermoses? A lot of the reviews on Amazon for the ones you recommended discussed mold issues in their reviews. Thank you so much! I appreciate you testing these products for all of us mommies!
Our team and families have never encountered any problems. As long as you wash them and dry them completely, you should be good. We’re glad you love these posts
Thanks for the video. Don’t think you’re supposed to microwave the lids on those glass containers, though. I always remove mine.
Hi Mo, the lid isn’t secured tightly on the container, it’s placed on top to prevent splatters.
I wanted to share this, but Facebook won’t let me. It’s flagged their security system, just FYI. Thanks for the great info.
I’m sorry about that, Mary! Did you click the Facebook “share” button or try to copy and paste the link into Facebook? It might’ve just been a one-time thing, so if you want to try again go ahead! Thank you!
Thank you so much for making this so easy for me! My son has swallowing issues and packing lunches can be difficult. I really appreciate the hard work you put into this by testing everything and sharing your info. I have no doubt that you have saved me so much time, money and frustration!!
I just got my son the 10oz funtainer. This week my husband is on a work trip, so I have to drop off my son earlier than usual. If I am putting his food in the container around 6:15 and he eats around noon will it be safe?
Funtainers are good for about 5hours, given that you heat the food as mentioned on the post.
I have been using Thermos Foogo containers for years with good success. To pre-heat the container, I add boiling water and screw on the lid while I heat the food. Just dump the water and refill with lunch and you will be goo to go!
Any suggestions on how to pack a thermos in a lunch box with cold items, such as juice box or yogurt?
Lisa from 100 Days had a whole post about how pre-heating the thermos has no effect on how the food keeps its heat. Thoughts?
While I respect Lisa and her process very much, I was curious about this. I took the time to preheat and test the thermoses as shown. The temperature is clearly different. To me, it is worth taking the minute to preheat.
Have you continued to use the Stanley thermos with success? Most of the reviews I read said they only lasted a few weeks before the seal broke. Evidently, they are now made in China, and the quality isn’t up to previous expectations. What has your experience been?
2 years going strong. the reason the seal breaks is because people are putting it in the dishwasher. The lid should be hand washed.
I struggle with keeping foods (other than soup) above 140 degrees from 7:15am to 12:15pm which is the time between when my sons lunch is packed and eaten. Any further advice? I’ve reheated spaghetti and marinara on the stove. I can only heat it to about a maximum of 180 degrees without burning it before putting it in a thermos preheated with boiling water. I’ve tested the temperature and after 2 hours using the funtainer thermos you recommended and it is in the neighborhood of 130 degrees which concerns me because for the remaining 3 hours it would be in the danger zone. I’m still so puzzled as to how to tackle a safe hot lunch. Thanks so much for your thoughts.
Rebecca, the foods we tested in our tests were heated in a microwave (sorry!) stirring often to prevent hot spots. As a mother of 3, I am less concerned with “safe temperature issues” in winter than summer. My biggest concern is where my kids’ hands have been (school bathroom… gross) rather than food that I’ve prepared at home and cooked it thoroughly the first time. Of course, you have to do what’s best for your family and I am glad you are testing this for your own precautions.
Thanks so much for your additional thoughts on keeping hot lunches hot and safe Laura. I too am most concerned about clean hands at lunch time. I actually pack a mini alcohol based hand sanitizer in my son’s lunch !
To keep lunches hot I heat food really hot, like said above. I also put boiling water in the canister to heat the container. And remove it, just before adding the food. That’s way your food doesn’t start cooling down right away from putting the food into a cold canister.
Exactly what I preach. Thanks Connie!
I just want to say Thank You for your suggestion about keeping my child’s food hot in a thermos. I wouldn’t have thought about it. My son is so happy that he can have other foods besides PB & J or bagels.
Thank you again. Can’t wait to see what other ideas you have.
Do you know of any rectangular container that can keep food warm? Something that the kids can open up and eat in like a small plate? I currently use a Thermos too but the mouth of the container is small. Short of using 2 Thermoses, is there one that can keep 2 different foods warm while keeping them separate? My son does not like the sauce or meats mixed with the pasta or rice.
I’ve searched everywhere an there are no square/rectangular thermos containers out there. I wish!
Do you keep foods besides soups warm? Weird question but my daughter loves sauteed shrimp and asked if I could pack her some in her stainless thermos. Do you think it would remain warm and safe even though it won’t be completely full? My husband is convinced that this is a horrible idea.
I use a thermos more often for other leftovers than just soup! A thermos is a wonderful idea. If your food was cooked to a safe temperature for dinner, reheating it and placing it in a thermos will be no problem.
Hey, C! Since shrimp take almost no time at all to cook completely, I’d recommend actually starting with raw shrimp in the morning. It might take an extra minute or two in the morning, but if you’ve prepped them for dinner, then they’re ready to cook.
Just make sure to hold boiling water in the thermos until ready to place the freshly cooked shrimp into it. I’ve done this myself for shrimp and seafood dishes, and haven’t had a cold. or otherwise unappetizing dish yet.
What if my child’s lunch time isn’t until 6-7 hours after? I leave for work in the morning at 6:15 AM, dropping him off at the extended hours program. (He eats breakfast there). Lunch isn’t until after noon.
I use a thermos too. The food will still be warm.
Should I still use cold packs inside the lunch box while packing a hot lunch in a thermos?
Yes. a thermos keeps the temperature hot inside. the icepacks are for the rest of the food (when needed)
I would like to know if any one has any suggestions on a food box or something to keep food hot, I,m going to do a food service driving round before I buy a jiffy van,
I’m sorry, I don’t know. perhaps you can go on amazon and look for those big delivery bags that the pizza people use?
The catering company my daughter worked for used regular coolers like igloo. They heated the food in foil serving dishes and stacked them in the coolers.
Does anybody has any experience using Mr. Or Ms Bento container kits?
No, I’m sorry. I prefer thermos containers or those made of stainless steel specifically for hot items
This may be a silly question, but his do you heat up the thermos? Is it microwave safe? The one I own has a metal interior.
I did see your post on how to heat up the thermos, thanks!!
I am looking for a good container for my husband that will hold plenty of food for him and keep it warm for quite a while. I was checking out the Stanley you shared about above and while reading reviews some people was saying that this was great at first and then lost its seal and wasn’t keeping the food hot for long, after only a month or so. I was wondering if you have experienced this at all? Thanks soo much, just found your site today (from 100 days of real food) and already love it!
Hi Nikki! Thanks for visiting us! I love that Stanley thermos. That’s the one my husband takes to work. The seal might of come off for other people if they wash and dry the lid in the dishwasher. I only wash the bottom of it, the top by hand. The “seal” is a rubber gasket/band and can come loose with high temperatures. I’ve had mine for over a year with 2-3x week use and no issues. :)
Why no onions??
they tend to stink the lunchbox, often make other foods soggy..etc.
You have mentioned heating up the thermos but most are stainless steel so can’t go in the microwave. How do you recommend heating them up properly?
Amie, check this post.
Thank you for this informative post! I love your site, and your newsletters. It is nice to follow you on Pinterest, as well, to see specific articles like this one on mornings when it seems like I need the advice the most! Your efforts for this experiment will help many, many Moms out there to pack great hot lunches! I do have one question – when I pack a Thermos with hot lunch for my kids I often don’t know what else to include with the entree. I am so used to packing items with a cold pack that I don’t know what accoutrements I can send with a hot Thermos full of, for example, ravioli with sauce. What items do you suggest?
Kimberly, pack anything else you would normally send. the thermos containers don’t absorb heat or cold from the outside. I send fruit, veggies and dip, some of the bars in our recipe section… a thermos is just a container… send the same items you would normally pack in another container.
Thanks for your response! Do you still use a cold pack to keep the other foods chilled?
I use a Packit for my kid’s lunches and we put the Thermos inside with the rest of the food. The food inside the Thermos stays hot just fine. We use the Funtainers.
So thorough, thank you for the great advice.
Excellent advice. I have the 10 oz. Thermos brand stainless containers plus another bigger stainless container that I don’t remember the name of. I always preheated the container by pouring boiling water in it. After dumping the hot water, I then added the hot soup. My daughter had no problems at all when she was young with this. Especially since she’s my soup kid. From when she was tiny to today, at 21, she will still eat soup before most other things.