This is not cheap, at around £10 for a tiny 35 ml bottle. But as Halfords no longer seemed to stock the Holt's Anti fog treatment I'd been using for years, I bit the bullet & bought some. The first time I used it, I was impressed. My visor inside stayed fog free for nearly a week, after one spray on a clean visor. On the o/side, rain ran off easily. The Holt's had required daily sprays. Next time it was not so good. My fault entirely, I had not made sure the visor was scrupulously clean & dry before spraying. Did so next time, & it was back to normal service. Well, it is pricey, but follow the instructions, & you will get a good few days for each spray.