Lidl Vacuum Flask
£7.99, holds 1L
Fairly basic model, with somewhat flimsy handle. Stainless steel construction with plastic screw stopper with pour option.
The weak point with all such flasks is that they lose heat through the top. For some reason the stoppers are wider than they used to be - and this seems to be the case on all new models i've examined including branded Thermos and Stanley.
I was pleased to see this model has two cover cups that fit together. This both adds an extra layer of insulation and means the flask comes with two cups rather than one, albeit that one is slighly larger.
I tested this flask by filling it with boiling water and left it for 12 hours. During the time the metal surface remained cold but the top did feel very slightly warmer than the sides, confirming my theory that heat is mostly lost through the top.
After 12 hours, the water was still quite hot. Probably just hot enough to make a cup of tea and slightly too hot for fingers, but not scolding.
Overall impressed for the price.