Flame Runner is a fire gear perk that raises your fire resistance after you slide. It rewards a fast, slide-heavy way of moving through burning areas.
After you slide, you resist fire better for a short time. Sliding through flames or into cover near a flamethrower soldier hurts less.
Situational. A permanent fire defense perk is easier to rely on, but this one rewards active players.
Flame Retardant and Fire Protection on other Fuego pieces round out a fire-proof loadout.