If I want to transport a litre of a hot liquid, what's the best option?

  1. Use a single one litre flask

  2. Use two 500 ml flasks. (Preferable due to the distribution of weight across two people).

Which option will keep the liquid warmer for longer (accounting for the fact that the liquid will be drunk at regular intervals)?

1 Answer 1


Theoretically, a 1L flask will keep the liquid warmer as there less surface area and greater mass.

However, in practise it is really a question of what size insulated (Thermos/vacuum type) flasks are available and how well they work.

Non-insulated flasks will not be much good in either case I would guess your liquid would definitely cool within an hour, and probably quite a bit faster.

For insulated flasks 1L ones seem to be the standard and many smaller ones are more mug designs which are not great for storing while walking, although I'm sure there are some which would work.

Other factors are two flasks are likely to be slightly heavier, due to the extra insulation needed. Which may be something to consider, I haven't looked what the likely difference is. Also weight can often be balanced through sharing other kit if using one flask.

  • 6
    1L will indeed keep the liquid hot for longer, but if you are using one flask at the time and not opening both simultaneously, liquid may stay warmer longer using 2 flasks. The more you open a flask the quicker it will get cold. Sep 8, 2015 at 15:43

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