Choose a Thermos

My wife wonders how large my thermos collection is going to get. A lot larger, I think.

We test each thermos to determine how it performs with leaks, heat retention, ease of use, cleaning, etc.

Here’s the minimum you need

  • Lined  with stainless steel (not glass or plastic)
  • Wide mouth (a narrow mouth helps with heat retention, but makes it harder to remove some foods and to clean)
  • Right size (thermoses are as small as 12 oz. or as big as 64 oz. Get the one that’s the right size for your family or use)
  • Quality name (we suggest using either Thermos brand or Stanley)

Heat Retention Tests

To see how different thermoses hold in heat, we tested them by pouring boiling water into each of them and then testing the water temperature after 1 hour, 12 hours, and 24 hours.

Here are the results:

1 hour 12 hours 24 hours
Thermos Nissan 34 oz. 199 172 149
Thermos Stainless King 40 oz. 198 169 147
Thermos Sportsman 40 oz. 199 167 140
Stanley Classic 32 oz. 194 160 139

13 thoughts on “Choose a Thermos”

  1. Definitely don’t get a cheap thermos! I tried cooking oatmeal in one and the top blew off after I closed it with boiling water in it.

  2. Thermos makes foodjar that I love. It’s stainless lined, holds 16oz, and has a squat shape and very wide mouth. My model doesn’t have the greatest heat retention rating, but it cooks nearly as well as my more expensive models. You can always wrap towels or wool socks around the moderately thermally challanged vacuum flask.

  3. Anyone ever hear of a vacuum flask with a stopper that’s not plastic? I dislike the idea of cooking in plastic bugs me.

  4. Pls explain your aversion to the glass model thermos.

    Also, any suggestions for smaller wide mouth thermos for cooking, say, one or two portions of oatmeal?

    Lastly, for the test comparisons to be fair & accurate, the thermos capacities should be equal. A smaller thermos will have an unfavorable surface to volume ratio, compared to a larger one. The larger one has the advantage because there is relatively less surface area for heat loss and it is also starting out with a higher thermal capacity.

  5. I have an el-cheapo stainless. Even with pre-heating the thermos (5 mins w/boiling water) and putting hot food in the flask, the food is not steaming by lunch time.

    I am wondering about food safety for the 16 oz wide mouth size. How many hours do the 16oz wide-mouth Nissan or Stanley keep foods hot?

  6. Is it possible to do the same with Quaker Old-Fashioned style oats, or just the steel cut?

    We’ve recently changed our diet here, and have been having lots of oatmeal for breakfasts. Its delicious, easy, and seems to stick with you longer. The only reason I ask is because I accidentally purchased a tub of old-fashioned oats for my ambulance station, when I wanted the quick oats for the m-wave. They don’t cook like the quick oats do, and now I’m stuck with an almost full tub of old fashioned oats…ideas?


  7. Mike, you can absolutely cook old-fashioned style oats as well. They’ll cook pretty fast in the thermos – I’d guess 20 – 30 minutes, but you’ll want to experiment a bit to get the consistency you like. Sloshing the thermos back and forth can give you an idea of what’s going on inside.

  8. If you search over time, you can find a used Stanley thermos, from the late 1960’s that use a cork stopper. I never bought it, but did in fact see one.


    Anyone ever hear of a vacuum flask with a stopper that’s not plastic? I dislike the idea of cooking in plastic bugs me.

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