Double insulation on metal bottles employs an inner and outer layer, often stainless steel, with a vacuum or insulating air layer in between. This design impedes heat transfer, effectively maintaining beverage temperature for longer periods. The vacuum or air gap acts as a barrier against both conduction and convection, preserving the desired temperature of the liquid inside.

Furthermore, this construction significantly reduces condensation on the bottle’s outer surface, preventing moisture buildup and ensuring a comfortable grip. Overall, double insulation enhances the functionality of metal bottles, keeping drinks hot or cold for extended durations while minimizing external moisture concerns.