Food thermos vs beverage thermos, which keeps heat better?

Lets compare the heat retention of a food thermos vs. a beverage thermos. As you probably know a sphere is the geometrical shape which has the least surface area to volume ratio.

A food thermos is typically lower and wider than a beverage thermos, making it closer in shape to a sphere. Meaning, if it has the same volume as a beverage thermos it has less surface area. And less surface means less heat loss.

But it's not that simple with a thermos. Since the cap is less insulated than the walls, and a food thermos has a bigger (and thinner) cap than a beverage thermos. Meaning the food thermos has more area which is less insulated than the beverage thermos.

For this experiment I got the most durable thermoses I could find, one Thermos Stainless King 16 oz. Food Thermos and one Thermos Stainless King 16 oz. Beverage Thermos. (Also available in bigger sizes.) According to the manufacturer they both keep the content hot for 12 hours and cold for 24 hours. Let's see if that's true!

I started by pre-heating the thermoses with hot water for a while. This should always be done if you want your drinks to stay hot longer. I then filled each of them up completely full and checked the temperature using an Analog meat thermometer. They were both 204.8 degrees Fahrenheit (96 degrees Celsius). I closed the caps and put them in slightly below room temperature, 66.2 degrees Fahrenheit (19 degrees Celsius) for 17 hours without opening them.

	Beverage thermos	Food thermos
Before
After

When I checked them again the temperature in the food thermos was down to 114.8 degrees Fahrenheit (46 degrees Celsius) and the beverage thermos was down to 136 degrees Fahrenheit (56 degrees Celsius). Note that this was a longer time than they are supposed to keep the heat. Meaning, the beverage thermos retains heat better than the food thermos.

So the winner is the Beverage thermos. I think this experiment very clearly shows that most of the heat in a thermos is lost through the cap, so when you look for a good thermos, make sure to choose one with a good solid cap like above.

If you want to see more tests like these, let me know in the comments!

I would love to hear what you think down in the comments.

The next upcoming article will be on choosing water repellant gear without sacrificing our environment, a truly challenging task! Like us on our new Facebook page below or follow us on twitter @sustainablebush to get notified when it's published!

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