How to Heat a Thermos

Thermos brand containers use thermal technology to keep cold drinks cold or hot drinks hot. The double wall insulation, provided either by glass or steel, traps the air inside so drinks to cool slowly or stay warm for longer.

While preheating the thermos bottle before filling it helps keep your hot beverage, glass or steel vacuum containers-ware may not be heated in the microwave or on the stove because the damage can occur to the outer balloon.



Open the faucet and let the water run until it becomes as hot as possible.


Fill the thermos with hot tap water. Screw on the lid so that the heat of the water escapes.


Leave standing water in the flask for 10 minutes to warm up the air in the space between the glass or steel thermal layers.


Empty the water from the bottle. Promptly replace it with your hot drink and put the CAP back on the bottle.


  • Thermos food jars also have a plastic coating and require the same preheating technique such as beverage bottles, because they are not microwaves.
  • Preheating technique works on any bottle of drink, including those that are not Thermos brand.