Molecule Labs Rain-Repel spray is formulated for use on the outside your helmet visor, goggles, or windshield. Simply spray on two coats and wipe clear to make rain run right off without sticking. You won't even need windshield wipers. 4 ounce pump spray bottle is enough for two to four windshield treatments, or dozens of helmet shields.
Note: Because of the wide variety of plastic formulations, always test any spray like this on a small area to determine compatibility first. Not for use on coated or mirrored shields.