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The Vacuum Flask Test

Like most of us I have collected a number of flasks during the years. Some were gifts some bought and others "inherited"

Last year I bought a couple of Lifeventure flasks, which according to the blurb were all singing and all dancing. Much as I was happy with these I found that when away on trips with Russell (Warthog1981) the performance of his flask seemed to be much better. Until then I had always thought that the performance of steel vacuum flasks would always be much the same. Well time for a test me thinks.

The Flasks
The flasks in the first set of the tests are as follows

From left to right
1) A 1 litre thermos flask that I have had for about 15 years. It is a model not made any more but looks similar to a model they still sell as a mid range flask that sells for about 20
2) A 0.85 litre Vango flask. A budget flask that sells for less than 10
3) A 0.75 litre GFF flask I got for free from Viking office supplies. Can't find a price for this but am guessing it is not high.
4) A 0.75 litre Lifeventure flask. Cost about 15 I think
5) A 0.5 litre Lifeventure flask. Cost about 10 I think

Now as the flasks have different capacities this test is not fair from the onset. My understanding is a smaller flask will cool quicker and that seems to be confirmed by the test but the results still show differences that would seem to be down to flask design rather than the size difference.

Test 1
I filled all the flasks with hot water to warm them and let them sit while I boiled a lot of water. The hot water was poured out and all flasks filed with boiling water at the same time or as near the same time as practically possible. Then the lids were put on. The cups screwed on the top and the flasks set outside in the cold and the rain to cool.

Five hours later I brought the flasks inside. Dried them off, and took the temperature of the water at the centre of the flask using a cooking thermometer. The results were
Thermos 85.9c
Vango 79.3c
GFF 75.8c
Lifeventure (0.75l) 82.9c
Lifeventure (0.5l) 73.4c

So from this first test the Thermos would seem to be the best but the larger Lifeventure was not far behind and may only be behind due to being a smaller flask. The Vango was in third with the GFF and smaller Lifeventure flask trailing behind.

Test 2
Now to make sure the results were accurate I decided to run the test again with the top three to make sure the results stayed in the same order. However, to simulate the conditions that the flask may get used in more accurately I make two changes. One was I did not preheat the flasks (when out on a trip you do not usually boil water to preheat the flask and then again to fill it). second I kept the flasks in my unheated garage so they were in the cold but not subject to rain as on a trip they would generally be kept dry. Also on this test I took the temperature after 5 hours and again after 15 hours had passed. The results are as follow

After 5 hours
Thermos 87.0c
Vango 75.4c
Lifeventure (0.75l) 79.1c

After 15 hours
Thermos 74.3c
Vango 55.5c
Lifeventure (0.75l) 61.9c

This test again confirmed the ratings of Thermos first, Lifeventure second and the Vango third. Moreover you start to see the benefit of the better flask. After 15 hours the Thermos flask has managed to keep the water at pretty much the temperature the Vango one is at after 5 hours.

A New Contender
Well now I could see that all flasks are certainly not made equal. I was surprised that a 15 year old flask was the one that was giving the best results. Moreover this is one of the thermos mid range models. How would one of their modern top end performers fare?

Time to find out. I ordered a Thermos 1.2l work flask. Thermos rate these as being able to keep water hot for 24 hours where as their standard range are rated for 8 hours. A claim like that just has to be tested. So enter the Work flask.

Test 3
Since I knew the top performer from the original selection of flasks was the old Thermos I only ran this test between it and the Work flask. I ran the test twice but the results were similar so I have only reported the first set.

For this test I preheated the flasks with hot but not boiling water and then stored them in an unheated building. I tested the temperature after 5 hours, 12 hours and 23 hours. the results were

After 5 hours
Old Thermos 90.1c
Work Thermos 93.7c

After 12 hours
Old Thermos 79.7c
Work Thermos 84.3c

After 23 hours
Old Thermos 67.2c
Work Thermos 72.5c

So the the claims on the Thermos web site seem to hold up. The Work flask takes an early lead and held about a 5 degree advantage. Of course you can debate whether you would still call the water hot enough after 24 hours but there is no arguing it is hotter than the competition.

Some thoughts
I will talk about the individual flasks and their attributes below but from the testing and my experience I have learnt some points. First there is a performance price to be paid for size and convenience. If you want the convenience of a smaller flask it will cool quicker. If you have a larger capacity flask that has thin walls, it will cool quicker. The Thermos flask (and the one Russell uses) are bigger than some of the cheaper flasks of the same capacity.

Convenience wise the easy pour lids that allow you to pour by pressing a button or lifting a tab seem to lose heat faster. I would like to have tested the Lifeventure flasks with a Thermos lid but it does not fit. When you take off the cup the Thermos Work flask lid was cool to the touch. The lids of the other flasks were all warm to the touch, a sure sign more heat was escaping this way. I would even be inclined to say the lids were probably the biggest factor in the different results.

I would also say the cost difference between the top flasks and the bottom is not that great. Given that these steel flasks last a long long time it seems worth getting a good one.

As stated the tests are scientific in that I took great care getting the readings but also subjective as the flasks are different capacities and were not tested in laboratory conditions.

The Flasks in Detail

The Thermos Work 1.2l

This is one of three models that Thermos rate as being at the top of the class. The others being the Rock and the Ultralight. I prefer this one to the Rock as the handle is less obtrusive. The Ultralight was more expensive so I opted for the Work as weight was not a huge issue.

I got the Thermos work from Tesco for 24.00 but I think you can get it a little cheaper if you shop around.

The flask is very much made to put up with a rough life. It has rubber reinforcing to help take the knocks and the outside shell is extremely robust. I can see why Thermos are happy to give a 10 year guarantee. Going by my other Thermos I can see this not being called on often.

As well as the body the places where the extra quality really shine are the lid and the cup. The lid just feels quality. It is hard to describe but you can just tell from the feel of it that it is well made and nigh on indestructible. Twisting the lid a half turn or so allows liquid to be poured from the flask. Not quite as easy as a push button option but still convenient and without the performance penalty of the alternative.

The cup is a sturdy, insulated and of a proper cup size and shape. Many of the flasks have strangely proportioned cups and the rest are usually to small. This is a cup I am happy to use and gives a decent size of drink.

All in all this flask is my number 1 overall choice. For performance and functionality it will be the one that goes with me on trips and full day paddles.

The Old Thermos flask

My old thermos flask most resembles the current Thermos Multi Purpose Stainless Steel Flask


And if it were not for the purchase of the Work flask for these tests it would be my flask of choice. I have taken this flask up mountains, to work and in the canoe It has been treated with no respect, thrown about and generally abused but taken all of this in its stride. This is probably true for all these flasks. The introduction of stainless steel vacuum flasks revolutionised flasks for the outdoors. I am sure I am not the only one who has thrown down their rucksack, at the top of a hill to hear their glass flask smash. At that time a steel flask is worth every penny.

This flask has the same design of stopper as the work flask but is obviously a few generations younger. It performs well but feels softer and does let more heat through. Of course after 15 years of use it can't really be criticised. It has nothing to go wrong which is good in something that you may come to rely on in the cold.

The cup is a bit thin and lets the contents cool pretty quickly. It is also quite wide and shallow. Perhaps this is to suit eating hot food from and perhaps it is just to suit the shape of the flask

The handle on the side folds in flat and seems gimmicky. I was pretty sure this would break in a few weeks. After 15 years I suspect it will not

So all in all a great flask and seems to explain why Thermos are still synonymous with vacuum flasks.

The Vango Flask

The Vango flask is very typical of the flasks that are widely available. The torpedo shape with no handle and the insulated cup fitting on top.
The only thing that makes the Vango stand out from the rest of these flasks is that it has a similar lid to the Thermos ones. I suspect it is this twist and pour top that gave the Vango the edge against the GFF and probably other flasks in this class.

For short trips this flask would do you well. For an inexpensive flask it does all it claims it will.

The GFF Flask
For some reason I forgot to take picture of this flask with its lid. It is similar to the vango flask but it has a push button mechanism on the lid. This makes pouring out liquid and then sealing the lid very easy. It does not feel very reliable though and I would worry about it breaking when on a trip. Of course I expected the Thermos handle to break and it has survived 15 years so this lid may do the same. More of an issue is it is almost certainly this lid that is letting the heat out of this flask and putting it effectively at the bottom of the table (the small Lifeventure is lower but almost certainly due to the capacity rather than quality)

The Lifeventure Flasks

The Lifeventure flasks are again the standard shape and style of flask. They have a tactile black coating that makes them a bit more grippy. The cups are very well made and the size is okay. A little small but each is in proportion to the flask it accompanies.

The lid has a lift up tab that allows you to easy pour liquid from the flask. While this is convenient it is something to go wrong. One of my flasks is already a bit temperamental. I use this on the smaller flask and this sees most use taking milk into Karen's shop so it is not getting hard use. The mechanism actually feels pretty well made but all moving parts are a concern.

As I have said I suspect that all of these convenience lids sacrifice some performance but this one seems to be not too bad. Still it would have been interesting to see how it would fare with a solid lid.

That said the 0.75 litre flask performed well and I suspect the 1 litre model would have been not as good as the old Thermos flask but not to far behind. When I am going out on the water for just a few hours and want enough hot water with me for a cup or two of a hot drink this flask is still likely to see some use.

In conclusion
All flasks are not equal

This review was first posted on our forum so if you have any comments or questions post them HERE

Song of the Paddle; The Call of the Open Canoe