Lexan is commonly used for helmet shields and windshields on motorcycles. It is a type of transparent, plastic or glass-like material that is scratch resistant and strong. It is stronger than glass. However, it can be scratched and often the visibility of Lexan windshields and visors is reduced by scratches. Cleaning Lexan can be done using official Lexan products but often these are quite pricey and for a motorcycle rider, the scratch may occur on a road trip where such products are simply not easily available.
Remove the visor from the helmet and lay it on a soft rag.
Trickle running water across the visor to keep it constantly wet. Wash off light dirt using just water and a soft rag. Soaps may create a haze of small scratches.
Squeeze a small amount of toothpaste (mild type) onto a soft t-shirt type rag. The amount should be just enough to cover the end of the index finger.
Move the toothpaste lightly against the scratch (side to side motion). The light abrasives in the toothpaste will reduce the size of the scratch by making smaller (less visible) scratches.
Rinse and check the visor frequently to note the results of the effort.
Dry with a soft dry cloth. (Do not use paper towels.)