The solution is toothpaste. One of my swimming coaches put me on to this. It is mildly abrasive. I just put some on my finger and rub in in the inside fairly hard. Then just rub it out under running water. I always rub spit on the inside of my googles before swimming and it works well. Sometimes have to renew the spit after 30-60 min but have never had to do that in a race. The one time I fogged in a race was ironman puerto rico when I had almost new googles and figured then wouldn’t fog and didn’t do the spit treatment.