Polycarbonate is usually a clear plastic -- often used for windshields, motorcycle fairing and airplane canopies -- through which operators can see clearly. Polycarbonate is an alternative to glass, as it is relatively easy to mold into complex shapes; however, it is more prone to abrasion, which gives it a fogged look, making it difficult to see through.
For regular, light-duty cleaning and polishing of polycarbonate, add water to baking soda to make a paste. You can also add Fuller's earth, a processed, consistent clay powder. Use the paste the way you use wax on your paint, rubbing it in a circular motion, rubbing it off, then cleaning the plastic with water or vinegar or a solution of both.
Sanding and Buffing
Polishing polycarbonate is conceptually the same as sanding a surface smooth. The only difference is, instead of a mirror-finish, you have a perfectly see-through surface if you do it right. Whereas sanding goes from course to fine grits, polishing goes from fine, to finer to ultra-fine. If you have more than surface scratches, you may have to gently sand the scratches out, beginning with 400-grit sandpaper and working your way to 1,000-grit or finer. After sanding, switch to a buffing wheel. Use slow speeds. Consider a very light abrasive like jewelers rouge, but note the manufacturers warnings. Excess buffing wheel speed, even with very fine rouge, can quickly create enough friction and heat to melt or deform polycarbonate. When in doubt, go slower and lighter.
MAPP gas and Acrylic cement can be used to polish polycarbonate edges, but don't try these approaches on the flat surfaces. MAPP gas has the correct heat range to easily melt polycarbonate. The edge smooths right as it begins to melt, just like butter as it begins to liquify. A very short heat pass can give you a polished edge. Chemically, acrylic cement wiped along the edge can do the same thing, but it's the cement that melts the polycarbonate, rather than a flame.
For additional materials, turn to a commercial polish or polishing system such as Novus' three-part polycarbonate polish. These products are often branded as "windshield polish." They contain a medium in which extremely fine abrasives (baking powder or similar to baking powder) are emulsified -- often in gradients like sandpaper.
These materials and these methods are unique to polycarbonate. They should not be used on any kind of coated plastic, and may not work on other types of plastic; in fact, they may damage styrene or acrylic.