For hot drinks:Start with a clean thermos. Warm your thermos by filling it with boiling water. Put the lid on. Let it sit for a few minutes then pour out the water.Once your thermos is warm, quickly add boiling hot drinks and put the lid on tightly.For cold drinks: Start with a clean thermos. Chill your thermos in the fridge or freezer. You can also fill the thermos with ice and water. Put the lid on. Let it sit for a few minutes to cool then pour out the water. Once the thermos is chilled, quickly add cold drink (at or below 4°C or 40°F) and put the lid on tightly.
