My next design idea that I came up is a two-compartment thermos. It can keep two different types of drinks both hot or cold simultaneously. For example: while preparing for the day in the morning, one will be able to carry both ice cold water and fresh hot coffee in the same thermos container. The water will stay cold all day, and the coffee will stay hot all day.
Here is a quick sketch:
This will be a good idea for those who like to have different drinks throughout the day, who are always out and about. It will also be easily washable, with the two compartments being removable.
This two-compartment thermos will be useless for those who only have one drink (whether it be coffee, tea, or water).