NAUI Open Water E-learning Practice Test

Fogging happens when moist air condenses on the cooler inner surface of the mask, forming tiny droplets that scatter light. Lowering the surface tension of the water causes that condensate to spread into a thin, uniform film rather than discrete droplets. A film on the lens lets light pass through more smoothly, so visibility stays clearer. This is the core action behind defogging methods like commercial defoggers or spit—both work by reducing surface tension. Using a mask with an anti-fog coating helps in the same way, but the essential effect is a lower surface tension that prevents droplet formation. Breathing through the nose doesn’t address the condensation on the lens, and simply changing water temperature isn’t a reliable, practical defogging method.