Plexiglass is not actually glass; it is a clear or opaque acrylic plastic material often used in place of glass. It is more lightweight than glass and not as dangerous when it breaks. One of the disadvantages, however, is that sunlight can cause detrimental effects, tarnishing or turning plexiglass a yellow colour from a combination of moisture, dirt and grime. Cleaning tarnished and yellowed plexiglass requires soap, water and some elbow grease.
Blow the loose dirt and dust off the plexiglass using a hair dryer set on cool. Blowing the dust off, instead of wiping it with a cloth, prevents it and dirt from working its way into the plexiglass.
Spray the plexiglass with a garden hose to wet it down. Spray from the top, and let the water run down to the bottom of the plexiglass
Fill a bucket with warm water and a few drops of dishwashing detergent. Avoid using glass cleaners since they are usually ammonia- or alcohol-based and can damage the plexiglass.
Clean the plexiglass with a soft lint-free cloth or sponge. Dip the cloth or sponge in the bucket, and gently scrub the plexiglass from the top down. Replace the cloth or sponge with a clean one if it becomes dirty.
Rinse the soap suds off the plexiglass with a garden hose. Inspect it for traces of yellow. If the warm water and dish detergent didn't completely remove the yellow tarnished areas, repeat the cleaning process using a stronger plastic cleaner. Follow the instructions on the container.
Rinse the plexiglass with a garden hose. Dry it with a clean lint-free cloth to prevent water spots that may develop if the glass dries on its own.