Thursday, December 1, 2016

Product Test: Thermoses

What do you know about vacuum insulation? What you might know by the trade name 'Thermos' is a broad category of drinking vessel that makes use of literally nothing to keep your beverage of choice either hot or cold. When I say 'literally nothing' I mean exactly that. Between the inner and outer walls of a vacuum bottle there is no foam, no water, not even any air; hence, nothing to transfer heat to or from you beverage. Does it work? That's what I sought to test. Let's go!

not your average bar
Drinkware, unite!
The following is a somewhat-scientific test of several different vacuum-insulated containers compared to non-vacuum containers. On the vacuum side we have HydroFlask, Stanley, Miir and Avex. On the 'other' side we have a plastic bottle, an aluminum bottle, a glazed ceramic coffee mug, and a glass pint glass. Scroll down to 'Conclusions' if you don't care about the data.

Hypothesis: Vacuum-insulated containers work better than non.

Method: Read temperature of vessel with IR thermometer. Heat water to boiling in electric kettle. Add about 8 oz. of hot water to vessel. Re-take temperature. Seal if applicable. Re-take temperature after six hours (two hours with non-vacuum vessels) and every two hours after until water is back to room temperature.

Results: Thermoses work. Here's what's up. All temperatures are in Fahrenheit and all fills are to 8 ounces with water.

Hydro Flask 12 oz bottle

Temperature empty: 67.2
Temperature with liquid: 158.6
After 6 hours: 120.9
After 8 hours: 110.3
After 12 hours: 96
After 24 hours: 77.3 (still noticeably warmer than room temperature)

MIIR 32 oz Howler

Temperature empty: 66.3
Temperature with liquid: 151.9
After 6 hours: 100.8
After 8 hours: 92.3
After 12 hours: 81.5
After 24 hours: 70.9 (pretty much back to room temp.)

Stanley 16 oz Travel Mug

Temperature empty: 66.1
Temperature with liquid: 146.8
After 6 hours: 102.4
After 8 hours: 94.9
After 12 hours: 83.9
After 24 hours: 72 (again, nearly room temp.)

Avex Highland Autoseal 20 oz Travel Mug

Temperature empty: 65.5
Temperature with liquid: 147.4
After 6 hours: 102.9
After 8 hours: 94.6
After 12 hours: 84.2
After 24 hours: 72 (nearly identical numbers to the Stanley mug, similar design)

Hydro Flask Vacuum Insulated Pint

Temperature empty: 69.7
Temperature with liquid: 139.3
After 4 hours: 76.4
After 6 hours: 68.3 (not nearly the performance with the open top)

Standard glass pint glass (aka what holds your beer at the bar)

Temperature empty: 69
Temperature with liquid: 134.3
After 4 hours: 70.4
After 6 hours: 66.9 (aka room temperature)

Ceramic coffee mug

Temperature empty: 67.8
Temperature with liquid: 131.3
After 4 hours: 69.2
After 6 hours: 66.9 (as expected)

Mizu single-wall aluminum bottle

Temperature empty: 67.2
Temperature with liquid: 146.8
After 6 hours: 68.6 (aluminum is a good conductor of heat)

Plastic Nalgene-style bottle

Temperature empty: 66.5
Temperature with liquid: 155.3
After 6 hours: 70.6
After 8 hours: 70.4 (plastic is not much better)

I did one more test with a 64 oz Hydro Flask Growler just to see whether having so little liquid (still 8 oz) in such a big bottle would affect performance. Here are the numbers. I'm not sure why I didn't test at the same intervals.

Temperature with liquid: 166.4
After 6 hours: 99.5
After 12 hours: 88
After 24 hours: room temperature (not as good as the Hydro Flask 12 oz)


Thermoses definitely work. Looks like the numbers are pretty close here, but Hydro Flask might have a slight edge.

Pro tips:

All of these bottles have been machine washed. A lot. Because I'm lazy. If you want the absolute max performance out of your thermos, hand wash it. At least if that's what it asks for.

One good way to get the best performance out of your chosen vessel is to prime it. If you want your coffee to stay hot for the max amount of time, pre-heat your thermos with some boiling water for a few minutes before dumping it out and adding the coffee. Starts hot, stays hot.

Fill it up. As you can see in the 12 oz vs. 64 oz Hydro Flask test, less air space leads to less heat loss. And why wouldn't you want to fill it anyway, right?

The Avex and Stanley models both have push-to-drink auto-sealing buttons. Klutz proof!

I tested heat because it takes less time for water too cool than it does to warm. These containers keep liquids cold even longer than they keep it hot.

Real pro Mark Sullivan (founder of Tailgate Alaska, among other things) suggests keeping a shitty thermos with you in your sleeping bag on winter camping trips. It trickles heat out all night long and that keeps you a little warmer in your bag.


  1. Which one do you carry in your pack when its cold and weight is at a premium?

  2. I'd go with the Hydro Flask. The simple plastic screw cap saves weight over the auto-seal varieties. The HF cap weighs just over an ounce (that's for the narrow mouth), while the Avex is 3.375 oz.