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MagiKelly

10-02-2008, 20:57

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

http://www.songofthepaddle.co.uk/flasks1.jpg

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.

http://www.songofthepaddle.co.uk/flasks2.jpg

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.

http://www.songofthepaddle.co.uk/flasks3.jpg

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

http://www.songofthepaddle.co.uk/flasks4.jpg

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

http://www.songofthepaddle.co.uk/flasks5.jpg

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

http://www.thermos.co.uk/products.php?prod=186291

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

http://www.songofthepaddle.co.uk/flasks6.jpg

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

http://www.songofthepaddle.co.uk/flasks7.jpg

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 ;)

gorilla

10-02-2008, 23:09

great review - may get one of the new thermos' for work

British Red

10-02-2008, 23:28

Fantastic review. I suggest a new rank of "Thermos Nerd" :D

I do like a small thermos that I have (about a pine size) - good for those 2 hour train trips to London - frankly so long as it keeps a drink warm that long it serves! I have a big one with a solid top for range days (no stoves allowed - especially when black powder is being shot - well duh!) - it certainly bears out your findings.

Fascinating!

Red

Tengu

10-02-2008, 23:29

This was fastinating, magickelly, thanks for putting in the effort

rik_uk3

10-02-2008, 23:56

Great post, many thanks:You_Rock_

MagiKelly

11-02-2008, 00:03

Fantastic review. I suggest a new rank of "Thermos Nerd" :D

Thank you but I blame Russell. Waking in the hammock in the morning to find the water a bit cool and listening to Russell in his hammock blowing on his coffee to cool it down was what set me off on this slippery road :rolleyes:

British Red

11-02-2008, 00:13

I blame Russ for all sorts of things but he just got another nice donation to H4H from some mates of mine for being a thoroughly decent sort so it must be your fault this time :)

big_swede

11-02-2008, 00:21

This was the most interesting thread in weeks. Great test Magikelly!

Shewie

11-02-2008, 00:30

An interesting thread John, I never realised so much could be written about a flask.

I have a Eurohike .75l which looks very similar to your GFF, it`s probably the same model with a different label on it. I find my coffee will stay hot for about 3.5 - 4 hours then steadily cool after that, becoming undrinkable after about 5. I make my coffee with milk rather than water and find that keeps it hotter, not sure if there`s any explaination for this though ??

Rich

MagiKelly

11-02-2008, 10:52

I never realised so much could be written about a flask.

Clearly you have never seen how much I have written about wellies ;)

In the next few weeks I am planning reviews of the Tay Sport Muck Boots, MSR Waterworks filter, MSR Dragonfly stove, the Powermonkey and a few more things. I realised I had a backlog of stuff I would like to review and some things I wanted to try and comment on so am making an effort to get on with it.

litefoot

11-02-2008, 11:34

Thanks, a great review,and you have persuaded me to update my flask.I do worry that you may have too much spare time,if there is a Mrs Kelly I would keep your flask facination very quiet or a hord of little jobs to do around the house may be coming your way!:D
Regards Litefoot.:)

gregorach

11-02-2008, 13:46

Yeah, good post MK!

Don't underestimate the importance of size - the volume to surface area ratio is exponential, not linear. It'd be interesting to test a selection of flasks that are all the same capacity... ;)

BorderReiver

11-02-2008, 16:41

The bigger the flask,the more room for extra insulation?

Or are they still "vacuum" flasks only?

Until you posted your review I hadn't even thought about the advances in flask design.

Nice one,cheers.:)

gregorach

11-02-2008, 18:27

Vacuum is the best insulation you're going to get. There could be a question about the quality of the vacuum I guess... But I think it's mainly down to the ratio of volume to surface area - all of the volume stores heat, but it can only lose that heat through its surface area. All else being equal, a larger object or container always has more volume per unit surface area than a smaller one.

(As an aside, this principle also means that the optimum shape for a vacuum flask is spherical. But that would be somewhat awkward in use... And it's also the reason why wee beasties need to eat proportionately far more than big beasties.)

BorderReiver

11-02-2008, 18:32

gregorach

11-02-2008, 18:39

BorderReiver

11-02-2008, 18:51

warthog1981

11-02-2008, 19:05

Thank you but I blame Russell. Waking in the hammock in the morning to find the water a bit cool and listening to Russell in his hammock blowing on his coffee to cool it down was what set me off on this slippery road :rolleyes:

i,ll give you a loan of my two flasks and you can include them in an update :lmao:

Glen

11-02-2008, 20:49

Yeah, good point... But I'm not sure how much practical difference it would make, especially since the inside of the outer surface of the flask is usually pretty strongly reflective in IR.

I strongly suspect that in practice a decent vacuum flask loses most of its heat via conduction around the neck and through the stopper. Which would explain my the flasks with the convenience stoppers seem to do less well...

I tend to keep my flasks stuffed between clothing in my bag and can very much notice the warmth of the fabric next to the flask(s), most of the warmth I feel is around the sides rather than at the top.
I suspect that one of the important aspects for heat retension is how the inner flask and outer walls are decoupled from one another and that most convection losses are through this decoupling. For sure some through the stopper, though that tends to have an air gap and a further plastic cup to offer extra heat buffering, whereas the decoupling link has has conductive steel either side of it, the outside of which is directly exposed to ambient temperature.

I guess sticking a flask in a very good insulator with strategically placed thermometers might give a good insight as to whats going on.

MagiKelly

11-02-2008, 21:02

I do worry that you may have too much spare time

Don't kid yourself. One thing I have to little of is free time. Just never underestimate the power of a compulsive nature ;)

i,ll give you a loan of my two flasks and you can include them in an update :lmao:

Bring this weekend and we can test them at Stoneliegh

MagiKelly

13-02-2008, 22:56

Tesco have a special offer on the Thermos Work flask. Half price for a limited period. At £12 these are a bargain.

http://direct.tesco.com/q/R.100-8295.aspx

SimonM

17-02-2008, 12:33

I've had the same flask now since I was an apprentice, so thats 22 or so years. It is an Aladdin Stanley, and if memory serves correctly is made to the same design and spec that US WWII bomber crews were issued with.

It has seen service on building sites across the country, 12 years or so service with the TA / Cadets and countless days out on the hills, and bears the scars and dents to prove it!

It is not the lightest of flasks, but still keeps my coffee hot till the end of the day, so is still my flask of choice, despite having a couple of lighter, Tatonka models.

http://i222.photobucket.com/albums/dd178/simonandbev/Equipment%20-%20general/DSC00406.jpg

http://i222.photobucket.com/albums/dd178/simonandbev/Equipment%20-%20general/DSC00407.jpg
Simon

Rebel

17-02-2008, 23:41

Thanks for the interesting review. I've also often wondered if the old glass flasks perform better than the stainless ones. I no longer have any glass ones to test my theory on as they all broke.

I wonder if there's an ultimate top of the range flask. I like the convenience of a half litre flask for carrying around but I have noticed that by the middle of the day it's not as hot as my larger flask.

There is also a large difference in prices. You can pick them up for a couple of quid in some stores like Poundstretcher or pay around £20 more for branded ones in more expensive shops.

I wonder if the 0.5 litre Thermos on special offer at Tesco right now performs better than my cheap one that does manage to keep the water hot enough for a coffee at lunchtime. The Work Thermos does come out well in your tests but it is also bulky for carrying around. The extra performance might be due to the thicker wall.

I don't have a great knowledge of physics but I presume heat retention in a vacuum flask is largely due to how well the lid creates a vacuum and reduces heat loss. There is also the problem of radiative heat loss. Glass flasks were much more shiny inside so I presume this is an advantage in heat retention over the dull interiors of stainless flasks.

The weak link in modern flasks seems to be the lid, especially the ones that pour without opening as they tend to break and allow heat to escape.

Hmm, maybe I should become a Thermos geek. :cool:

Tiley

20-02-2008, 15:02

Interesting review. Has anyone tried out the Tatonka vacuum flasks? My only reason for asking is that they came out top in a recent(ish) review in "Trail" magazine.

SimonM

20-02-2008, 18:12

Hi Tiley,

i have the Tatonka 1l steel flask, and it does what it says on the tin - veery good flask IMHO.

As I stated in my post tho, I prefer to use my Aladdin Stanley, mainly becasue we have "history" and I'm a big softy at heart!

Simon

Graham_S

20-02-2008, 22:50

I've got one of those aladdin stanley flasks, I got it years ago in a NAAFI in cyprus with a couple of insulated mugs.
cracking piece of kit.

Rebel

20-02-2008, 23:41

Okay I did a quick test on an unbranded 0.5 litre vacuum flask. I've had this one for five or six years. I can't remember where I bought it or when or how much it cost but my guess is it was on special offer in some kind of store like Wilkinsons or Poundstretcher. I reckon it was less than a fiver, probably around three quid.

It has a mechanism that you push down in the lid to pour water and then you push an outer ring and it locks back. This mechanism looks fragile and when I bought it I thought it would only last a few months but it has lasted years.

For my test I thought I should clean out the limescale and when I did it looked a lot nicer inside. I poured boiled water from an electric kettle into the room temperature flask. I took a thermometer reading of the water I'd just poured in (I used a food thermometer so the readings aren't very precise) and the temperature was 95C (not 100C).

Four hours later (this would have been about the amount of time until my coffee break) the temperature had dropped from 95C to 76C - not quite hot enough to properly brew my fresh ground coffee really (so that's what's been wrong with my coffee breaks :p ).

I tested the temperature again 81/2 hours later (should have been 8 hours but I forgot) and the temperature had dropped a mere 57C.

ghems

09-04-2008, 17:18

i have found that for longer trips out only keep water in your flask...
it reduces staining and tainting and you get to start from home with a pre-heated flask containing boiled water.......

At every opertunity use the boiling water from the flask in your billy to make your brew. Top this up with cold when reboiling for the brew so that you can refill your flask with boiling water again.

This ensures you have a full flask at all times and you use less fuel when making a brew as your stating water is hot.

It leaves you with a flaskful of hot water at all times and has the bonus of taking less time to brew up on the stove/fire.

BorisTheBlade

05-01-2011, 15:45

Excellent thread, thank you!