How long your drink will keep its temperature in your vacuum flask will depend not only on what kind of flask you are using, but also the size of it and what temperature it has when filling up the flask. On the left, you can see three different graphs showing how the temperature will change during a period of 24 hours in our Vacuum flasks, Make sure the beverage is 97° C when first pouring it into the flask. Notice how it differs when comparing a 0.35 liter flask with a 1 liter flask.