Thermoses allow us to switch things up and enjoy a nice hot lunch, whether it’s your favorite leftovers or homemade soup or even keep items like smoothies or yogurt parfaits chilled!
The questions “how long is it safe to keep my food hot in a thermos?” and “how long will food last in a thermos?”, or “what thermos containers are best?” are notable concerns for many parents packing school lunches.
Properly packing hot and cold food into a thermos container is essential in ensuring that your food will be safe to eat by the time lunch rolls around so let’s go over both methods. Since packing cold foods is super simple, we’ll start there.
When it comes to packing milk, smoothies, or a yogurt parfait as long as the food does not sit at a temperature above 40F you are good to go. Before packing cold food, you do need to chill the thermos, which can is done by placing the thermos container in the freezer overnight, once your food is packed and sealed place it in the lunch bag along with a freezer pack. Ta-da!
Now onto the hot meals! Ever heated your food in the morning, packed it in a thermos and by lunch it’s was cold? Yup, me too but before you throw away that thermos container watch the video below to see if you are correctly packing hot lunches.
As you saw in the video, before packing hot food into a thermos, it needs to be HOT! Remember that hot lunch we talked about earlier? Yes that one, well it’s likely that your food wasn’t properly heated before being packed into the thermos. The good news is that there is nothing wrong with your thermos, hoorah!
How long can food last in a thermos and still be safe to eat?
Given that you cooked the food to a safe temperature and then warmed it up to a piping hot temperature, the food inside the thermos container is not likely to go bad.
But because I love you guys, I’ve researched proper food preparation and storage so that you can safely pack hot lunches for your family! Here’s what I’ve learned:
- Bacteria grows quicker between 40F and 140F, so perishable foods should NOT stay at that temperature range longer than 3 hours (therefore, hot foods should be heated to 212F a.k.a “too hot to handle” before packing in a thermos).
- Thermoses must be preheated before filling. This step often skipped, but it’s easy to do and worth it on cold winter ways when you want to pack leftover homemade Mac and Cheese or Chicken Alfredo.
How to Warm a Thermos
If your food isn’t keeping warm as long as you thought, you need to pre-heat your thermos container. Here’s how:
1. Boil water
2. Fill thermos container with boiled water, cover.
3. Wait 5 minutes and warm food in the microwave while waiting.
4. Empty the thermos
5. Place piping hot food into thermos, close.
6. Pack and enjoy!
Food packed inside any lunch container should be thoroughly cooked through, so no raw eggs, onions or undercooked meats or raw fish.
How to Keep Food Cold in a Thermos
Now that we know what to do with our thermos soups, pastas and leftovers, the question remains – how can you keep food cold in a thermos? If you are packing smoothies or yogurt, you’ll want to make sure those things stay chilled to temperature as well. Here’s how to make sure your cold food stays cold in a thermos lunch.
1. Place thermos in the fridge with some ice water inside it to chill
2. After thermos has chilled, put your smoothie, drink or other cold food items into the thermos and pack it in the lunchbox
3. Place the thermos near an ice pack in the lunchbox to make sure it stays nice and fresh until lunchtime.
How to Pack Hot and Cold Items in the Same Lunchbox
One question I get asked all the time, is if hot and cold items can be packed in the same lunchbox. The answer is, absolutely they can! This is one reason I love using large, square lunchboxes, it helps make sure I can get everything my kids need for lunch, in one simple carrying case.
Watch how easy it is to pack hot and cold lunch items together in the same box:
Now for the thermos testing.
Below are my four thermos container recommendations. Each container was tested three times with the same method: Heating soup to 210F, packing it into the thermos and waiting 5 hours before checking the soup’s temperature. The results:
Thermos Funtainer 10 ounce
Great for kids, easy to open and fits a good portion of food – 1 ½ cups! The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 138F –perfectly warm and good enough to eat.
Buy the Thermos Funtainer here.
Thermos FOOGO Stainless Steel 10-ounce
Thermos FOOGO Stainless Steel 10-ounceSimilar to the Funtainer (with the exception of a rubberized grip) and great for kids. Totally worth purchasing! The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 134F.
Buy the Thermos Foogo here.
Lunchbots 16-ounce
I love and own this one merely for the size. It has a wide opening which makes it more like a bowl and easier to eat out of. However, it can be a little more difficult for younger kids to open because of the wide lid. It also holds a lot of food, 2 cups!
The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 130F.
Buy the Lunchbots Food Jar here.
Stanley 17-ounce
This one WORKS! The temperature of the soup was 210F when placed into the thermos, and after 5 hours, it was 165F!
It was almost too hot to eat, but after a few minutes of being open, the soup was perfect! It’s also great for both kids and adults, easy to open and since it’s 17 ounces that means more room for food, about 2 cups.
Buy the Stanley Insulated Jar here.
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?
mycfavisit
This article is too informative. I really recommend to my friends and family.
MOMables-Laura
Thank you!
Melissa
Thank you!!! Appreciate your thorough information!!
Jamie
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.
Azucena
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!
Lyndsy
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.
Mike
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.
Jillian
Hi, I’m just wondering how exactly you preheat the thermos? (I’m specifically looking into the Stanley one)
MOMables
They all really work the same. Here is a link to an older post: https://www.momables.com/how-to-warm-a-thermos/
Jan
Hi,
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.
Thank you,
Jan
Stephanie Schneller
This would not be safe. Stainless steel cannot be heated in a microwave.
Lakshmi
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?
MOMables
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!
Kristin Suyanto
Hi Laura,
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 :(
Suzanne Bare
Thank you for this post – it had just the answers I was looking for!!
Emilie Hebert
Awesome!!
Becca
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!
Emilie Hebert
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
Mo
Thanks for the video. Don’t think you’re supposed to microwave the lids on those glass containers, though. I always remove mine.
MOMables
Hi Mo, the lid isn’t secured tightly on the container, it’s placed on top to prevent splatters.
Mary
I wanted to share this, but Facebook won’t let me. It’s flagged their security system, just FYI. Thanks for the great info.
MOMables
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!
Tahmina Amos
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!!
Jessica
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?
MOMables
Funtainers are good for about 5hours, given that you heat the food as mentioned on the post.
Julie Moussot
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!
Brittany
Any suggestions on how to pack a thermos in a lunch box with cold items, such as juice box or yogurt?
Rachel
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?
MOMables
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.
Karen Lynne
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?
MOMables
2 years going strong. the reason the seal breaks is because people are putting it in the dishwasher. The lid should be hand washed.
Rebecca
Laura,
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.
MOMables
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.
Rebecca
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 !
Connie
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.
MOMables
Exactly what I preach. Thanks Connie!
Stephanie
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.
Rosa
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.
MOMables
I’ve searched everywhere an there are no square/rectangular thermos containers out there. I wish!
C
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.
MOMables
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.
Laurie
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.
Anna
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.
MOMables
I use a thermos too. The food will still be warm.
Sunetra
Should I still use cold packs inside the lunch box while packing a hot lunch in a thermos?
MOMables
Yes. a thermos keeps the temperature hot inside. the icepacks are for the rest of the food (when needed)
Erica munden
Hi
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,
Ericaxx
MOMables
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?
Kelly
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.
Jorge
Hello,
Does anybody has any experience using Mr. Or Ms Bento container kits?
MOMables
No, I’m sorry. I prefer thermos containers or those made of stainless steel specifically for hot items
Ann Marie
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.
Thanks
Ann Marie
I did see your post on how to heat up the thermos, thanks!!
Nikki
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!
http://www.amazon.com/Stanley-17oz-Classic-Vacuum-Black/dp/B0019D7AGE/ref=lh_ni_t?ie=UTF8&psc=1&smid=ATVPDKIKX0DER
MOMables
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. :)
brittany
Why no onions??
MOMables
they tend to stink the lunchbox, often make other foods soggy..etc.
Amie
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?
MOMables
Amie, check this post.
Kimberly
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?
MOMables
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.
Kimberly
Thanks for your response! Do you still use a cold pack to keep the other foods chilled?
MaryB
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.
Rashelle
So thorough, thank you for the great advice.
Debbie W
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.