Most cheaper flask's perform reasonably well in my experience.
Biggest problem with most , is that they leak as the seal fail due to growing or distortion or shrinking!
Currently using a cheapo Tesco 0.5ltr stainless steel flask. (£3 in a sale)
Fits in a bottle cage.
Only negative is the cup is too small, so carry a plastic polypropylene std size cup.
I only fill the flask with boiling water after pre heating it.
Get two drinks from it.
I commute 35+ miles each way to work.
Stop at 25 miles (it's cold and dark now!) for a instant 3 in 1 coffee or a tea. (250ml) then one at lunchtime about 7hrs after filling it. Still reasonably hot.
By the way ,it's not light!
I have bought a few expensive branded flasks over the years which perform no better and in a few cases far worse!
For proper rides in this cold weather I have the 1ltr version (4 cups)
I usually strap it to the fork or rear rack with a piece of inner tube slid over it to stop rattles and paint/metal damage.
Hope this helps!

I did some home science with the kids, to assess the performance of our various insulated flasks.

Thermos Ultimate comes out on top. As expected, the 900ml one performed better than the 500ml one.

Surprise finding was the good performance by the old school glass-lined Thermos Mondial model, which is much cheaper, though also heavier and much more breakable. But I have found that glass bottles are bit more resistant to the accumulation of a gamey, thermos funk that is a hazard if you regularly fill your flask with pre made coffee and tea. I tend to use my metal lined ones for hot water, and brew on the road. Also interesting was just how badly the no-name stainless flask performed.

Hope this helps!

Good work Jack

2 pages on the merits of flasks, old age isn't as bad as I thought

In the interests of completeness I'd like to put the Thermos Ultimate head-to-head with one of the Zojirushi models, which are the only other flask/insulated mugs seem as highly rated. But I don't have one. But I don't really see that there's any real world need for better performance than the Thermos Ultimate.

The flask is due for a revival. I am so tired of all people on Instagram busting out their gas canisters and moka pots for the camera.

That chilly one is shocking

Have been using an Elite Mia bottle for the last two months (gmfits a standard size cage) and it keep the drinks really warm. Used it last week, didn’t prime it and 8 hours later of being left outside, it was just the right temperature to drink

Well I got a thermos ultimate and its great. Getting the instructions out of it was really difficult....

Oi, don't set him off

fatbikephil wrote: ↑Sun Dec 26, 2021 11:34 am Well I got a thermos ultimate and its great. Getting the instructions out of it was really difficult....

Add hot water.- they float out if they haven't dissolved...