A partial (or flash) mirror coating adds a lighter reflective layer to the outside of your goggle lens. It cuts some glare and gives a subtle mirror look, but it doesn't block as much light as a full mirror coating. Think of it as the middle-ground option.
This makes partial mirror goggles ideal for variable conditions—those days when the sun comes and goes, or when you're skiing in moderate brightness. The coating only reduces visible light transmission (VLT) a small amount, so you still see well when clouds roll in or light goes flat. It's a versatile choice if you want some glare help without committing to a full sunny-day lens.
Partial mirror coatings are also more forgiving than full mirrors when it comes to scratches and daily wear. You still need to clean them carefully—never wipe with a dry glove or rough cloth—but minor scuffs won't stand out as much as they would on a highly reflective surface.