As best as anyone knows it's the silicone which reduces the surface tension so large bubbles can't form. I regularly use it in my fuel whenever I make a new batch (one quick squirt in 5 litres). There are stories that it can foul plugs but it's been used here in Australia for more years than I can remember and I've never heard of any complaints about plug failures, in fact some time ago I made up a tank of fuel with enough Armor All to treat maybe 40 gallons of fuel and the plug survived perfectly.