Advice to maximise the performance of your isothermal bottle.
The fuller the flask, the better it is at keeping the contents hot or cold.
Be careful when using hot liquids, the flask is extremely well insulated, liquids will remain hot for a long time!
We use a double stainless wall with a vacuum between to block thermal exchanges by conduction or convection. To block exchanges by thermal radiation, a fine layer of copper covers the outside of the inner wall.