Whether you're swimming among coral reefs and bright fish, racing in a swim competition or feeling the wind in your hair on a motorcycle, having your goggles fog up can put a big damper on an otherwise fun time. If you're not willing to pony up the cash to try one of the many defogging solutions out there, you have a number of things to try, using ingredients you likely have at home.
Perhaps the most accessible solution for defogging your goggles is right within your body: saliva. This is an old trick used by swimmers to keep their goggles clear while under water. Spit a small amount of saliva into the inner portion of the goggle, spread it around, and then let any excess drip out. Repeat the process for the outside of the swim goggle. While this treatment typically doesn't last more than one round of swimming, it's easy to do and shouldn't be too much trouble to repeat before every swim session.
According to the Hawaiian snorkeling resource Kihei Beach Bums, applying baby shampoo to your goggles before swimming can also reduce fog. Kihei Beach Bums recommends adding a drop of tear-free baby shampoo directly to the inside of your goggles just before swimming. Spread the baby shampoo around, and then give the goggles a rinse in the water. You can also create a spray-on solution using one part baby shampoo to five parts water. Add the solution to a spray bottle and spray on just before getting into the water.
Apartment Therapy recommends using a vinegar mixture as an anti-fog therapy for bathroom mirrors. You can also try the solution on motorcycle or swim goggles, since mirrors experience fogging for the same reason: excess moisture. Place 2 tablespoons of vinegar in a bowl of hot water and stir around. Then dip a lint-free cloth into the bowl, wipe inside and outside of the goggles and allow to dry. Do not wipe off the solution with a dry cloth, as this will do away with the anti-fog application.
According to researchers at the University of Western Australia, another home-grown solution is to use a potato. Researchers extracted the juice of a potato and wiped it onto their visors to test it, but you can create the same effect by cutting a potato and wiping it on your goggles. Allow the juice to dry, and then use a cloth to wipe off any cloudiness that may be impairing good vision within the goggles.