How to more than double the insulation temperature time on your vacuum flask for hot liquids

Most of the heat escapes a vacuum flask through the lid, placing a sheet of aluminium foil over the sealed lid, secured with rubber band will double the time your tea, coffee or soup stays “stove-hot.” I personally clocked near boiling water stay steaming same temp hot for 2.5 hours, before I opened the lid to end the experiment, more than double the usual insulation time, without the cover.

It is also a good idea to “prime” the flask or tumbler with hot water (add and discard) to heat the interior before putting what you want in it.