Plastic convertible rear windows that have been subjected to the elements can fog up due to oxidation, water stains, sunlight fading and heat exposure. Plastic windows eventually lose their pliability (oils and elasticity), suffering dryness and cracking as a result. Cloudy residue on the plastic windows obscures a driver's visibility, severely limiting perception and the approach of oncoming or passing vehicles. Vehicle owners can restore their plastic windows with patience and a few basic tools.
Park the vehicle and set the emergency brake. Raise the convertible top and lock it into position. Wash the outside of the glass with soap and water, removing all dirt and grime. You can also sponge off the inside of the window. Buff both surfaces dry with a shop rag.
Don your rubber gloves. Apply a liberal amount of the coarse-grade compound to the emory paper or abrasive cloth. Begin at one end of the window, applying pressure on the surface with circular motions. Flexing four fingers downward with one hand supplies an even pressure over a small surface area. Do not use the heel of the hand to push against the surface. Medium pressure works fine. Polish from one end to the other then back again. Repeat this process for the interior side of the window but use less polishing force.
Use the medium-grade of plastic polishing compound to make the next pass over the window. Do not be concerned if the window appears fogged or hazy; this is residue from the compound, which is natural. At this point, you will be able to see small scratches. Concentrate on removing all scratches with this second pass, using medium-pressure, circular polishing strokes. When finished (inside and out), wipe as much residue away as possible with a shop rag.
Use the fine-grade compound for the last round of polishing. Look for any small scratches you might have missed with the last pass. This step will begin to remove the compound residue. Keep polishing in one area until you see some transparency. You may want to alternate between the inside and outside surfaces to complete a large section. Wipe the area clean with a shop rag when finished. Use a microfibre towel, and buff the entire surface (inside and out) until you achieve a clear lustre.
Apply car wax to the inside and outside of the window if you want added protection against water and other contaminants.