Thermos Flask Failures and Deconstruction

A dent will not render the flask useless. The outer or inner wall needs to be punctured for the flask to fail. A vacuum is the best form of insulation however, if you want to purchase a less efficient foam insulated flask then you wont have any further problems.
Alternatively, you could make sure the flask is transported in such a manner as to protect it from 'dents'

I still have my original stainless thermos given to me when I started my apprenticeship 30 years ago. To say it is dented is an understatement. It still dispenses coffee That is too hot to drink. My old boy still has his green hammertone Stanley flask which is older but in better condition. They still sell both models I believe but you’ll be set back $80-100 odd for a decent one.

I got sick of luke warm Thermos based hot drinlks years ago - I now use one of these

Jetboil

Given up on thermos for the same reasons as you.
I use one of these, tough and reliable and also heats our shower water.

Pedro1
Did you find out why? seeing cutting them open was to find out the reason. Why did they fail,? Has that been determined? you may not have confidence in that brand but unless you found out why then it is trust with any future purchase.

As a full-time Thermos flask user since 1965, I can tell you this much - I have never, ever found a full-metal construction Thermos of any brand - and I've bought and used them all - to be of any major usefulness in keeping hot water hot.
Even the Stanleys I've bought were next to useless, with boiling water poured into them at 5:00AM or 6:00AM, being just lukewarm at midday on most days.
Even pre-heating them with boiling water did little to improve their effectiveness.

I found that the cheapest glass Thermos from K-Mart or Target or Coles or Woolies (when they still sold them) were the best Thermos' for keeping water hot.
The only problem is their fragility, and they need extra-special care.
I missed out on hot drinks more than once by leaving the glass Thermos on the ute seat, and braking hard to avoid animals, sent the flask crashing to the ute floor, destroying it in the process.

But the bottom line is that the cheap glass flasks are not a great financial loss if broken, and they are quickly replaced by another el-cheapo Chinese flask.

I currently have 2 x 1 litre all-metal Aladdins bought from Bunnings in Broome last year, and they have only re-inforced my view, that these style of flasks are useless.
I wouldn't have bought them, but the missus won out because she liked their size.
Even preheating for 10 mins with boiling water and then emptying and refilling again, in the early morning, they are only just barely warm by midday.

Cheers, Ron.

Since my double wall Thermos style failed, I keep it, full, in the engine bay. Aeropress coffee is best made with about 90 degree water.

Send an email complaint to Rudolf Clausius.

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Pedro,

I am finding some confusion here with the "inner and outer" walls.
There are three walls.... the inner wall of the vacuum flask, the outer wall of the vacuum flask, and the outside shell that surrounds the whole appliance. It is difficult to determine which you are referring to.

I can only imagine that any "dents" are occurring in the outside shell of the appliance. If this dent touches the wall of the vacuum flask then some, but I should think very little, heat transfer would occur.

If impacts to the outside shell are of such magnitude as to dent the vacuum flask outer wall to contact the inner wall then that is a mighty solid impact and may be considered as rough handling. Maybe Thermos are pretty flimsy but my old Aladdin Stanley is scratched and rusty, but not dented and seems to have a pretty solid outside shell that manages fair handling. Maybe later models are more flimsy?

Incidentally, my first Stanley lost vacuum soon after purchase and was promptly replaced by the manufacturer without question.

The 1.8L "Nissan" Deluxe Thermos was recommended to me about 15-20 years ago. Cost over $100 back then but you can still get them for similar money. I carry two of them as our hot water system - I heat water on the fire then use the water for drinking and washing. Tested them last year and both still work as well as the day they were bought