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 in
the first set of the tests are as follows
From left to
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
4) A 0.75 litre Lifeventure flask. Cost about £15 I think
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.
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.
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
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.
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
Lifeventure (0.75l) 79.1c
After 15 hours
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
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
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
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
Work Thermos 93.7c
After 12 hours
Work Thermos 84.3c
After 23 hours
Old Thermos 67.2c
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.
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
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
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
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.
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.
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.
Old Thermos flask
thermos flask most resembles the current Thermos Multi Purpose Stainless Steel
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
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
So all in all a great flask and seems to explain why Thermos
are still synonymous with vacuum flasks.
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
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.
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 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
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.
All flasks are not equal
This review was first posted on our forum so if you have any comments or questions post them HERE