Straight from the smith website and plenty of other sources. the 5x refers to the fact that they made it 5 times bigger.
'A hydrophilic chemical treatment creates a micro-etched surface on the inner lens to absorb moisture before fog can form. Because Fog-X is a treatment that is actually burned into the lens, it canít be wiped away like other anti-fog coatings.'
Much appreciated. I feel more comfortable now touching the inner lens with a micro fiber cloth.