HEWER MultiBOT water bottles not only keep water hot, but also keep water cool

That is the magic of vacuum insulation. While we often call them "flasks" or "thermoses," the technology inside doesn't actually care about the temperature of the liquid, it only cares about stopping heat tranfer.

Here is how a single bottle can pull off both tricks:

The "Vacuum" Secret

HEWER MultiBOT water bottles are made of two stainless steel walls with a literal vacuum sealed between them.

Heat needs a medium: Heat usually moves through solids, liquids, or gases (conduction and convection).

The Void: Because a vacuum contains no air, there are no molecules to vibrate and pass the energy along. The heat gets "trapped" on whichever side it started on.

Why It Works for Both