Imagine you are making tea using a teabag, in a cup. You add the hot water and wait.
The strength of the tea increases as the water makes contact with the leaves, but the temperature of the tea is decreasing, because it’s in contact with the surroundings.
Today’s invention is a cup which allows the user, who knows how long his favourite brew takes (assuming it starts at 100 degC), to have his tea stay above a certain temperature until it has brewed. It is made of a series of insulative, concentric cups, with only the innermost holding tea.
If you know it takes thirty seconds brewing time to make your ideal tea, then you need not worry about cup insulation and can go eg with the left hand arrangement.
If, however, it takes 2.5 minutes, then you may want to select a different level of insulation, such as the one on the right.
A more sophisticated version of this would include a viscous-flow timer, based on tight fitting cups, with variable sized vents. The weight of the tea would cause the series of cups to fall into each other slowly in a repeatable process which could optimise the final temperature for an individual.
So I might choose to open hole 1 in cup 1, hole 3 in cup 2 and hole 2 in cup 3. This would cause the cup to take my preferred 3.1 minutes to fall, whilst keeping the final temperature about 89 degC.
See also this.