Here's what
LP Plastics, "the world's largest manufacturer of light aircraft windshields and windows", recommends. As the original subject was Pledge, I've highlighted what they say regarding furniture polish. It echos what other posters have already said.
When cleaning a window, always remove as much abrasive dirt as possible without touching the surface. Ideally this would involve flushing the surface with water and allowing the accumulated bug residue to soak, possibly with a little dish washing liquid added to the water. If a little rubbing is needed, do it lightly with your bare hand. After a final flushing with more water and carefully drying with a clean soft cloth, use a good grade cleaner/polish intended for acrylic windows, following the manufacturers directions.
We need to step back here and take a look at cleaner/polishes. Everybody seems to have a favorite, from great and proper to poor and very dangerous. The good ones, at least those that are safe to use on acrylic plastics, tend to be the commercial ones, intended to be used on this specific material. The bad ones, including the very dangerous, tend to be materials never intended to be used as an aircraft window cleaner/polish, such as glass cleaners and furniture polish. Glass cleaners invariably contain ammonia, a killer of acrylics. DO NOT use anything containing ammonia on acrylic plastics. It will cause crazing (thousands of microscopic cracks) in short order. Furniture polish seems to be safer, but its long term use is undocumented and reports indicate it builds up and produces smears that are hard to polish off. Something to consider about furniture polish - it is intended to be used indoors, not outdoors, and on furniture, not aircraft windows. Furthermore, it's not much less expensive than many aircraft window products.
Good and safe care products vary in their ease of use and other properties, so if you don't like what you're using, give another a try. Talk with other pilots about what they are using, but be sure the product you select is intended for acrylic windows. Other products to keep away from your windows include any aromatic solvent, such as methyl ethyl ketone, acetone, lacquer thinner, gasoline (a minor fuel spill should do no harm), and, heaven forbid, paint stripper. If you have to remove masking tape residue or other sticky or greasy stuff, the safest solvents are 100% mineral spirits or kerosene. Some alcohols are safe, such as isopropyl alcohol, but not all.
Concerning the polishing cloth, use the softest cotton cloth available. One hundred percent cotton flannel is ideal and available in yard goods stores. Old washed-out cotton T-shirts are a good second choice. We at LP Aero Plastics have never found a paper product that did not scratch, even those advertised for cleaning plastics. One benefit of cotton cloth is that it can be washed, thereby effectively recycling the material.
Your choice of cleaner/polish should also be based on what is needed. Basically, you have to determine what type of care is needed and pick the best products to do the job.
First, it's best to understand what types of products are available. They can be loosely grouped into three categories:
1. Non-abrasive liquid sprays, in pumps or aerosols, that may or may not have scratch filling properties.
2. Non-abrasive creams that have scratch filling properties.
3. Mildly-abrasive creams that have scratch removing properties.
Since windows do accumulate minute scratches as part of everyday life (the kind you can't feel with a fingernail but can really see when flying into the sun), the products that fill fine scratches are great for regular use. If scratches still appear when flying toward the sun, the abrasive variety and some elbow grease is called for. This type of cleaner should be used occasionally only as needed. Most manufacturers of abrasive cleaners recommend following up with a scratch filling product as a second step.
The bare hands folks find support from the FAA. AC43-13-1B, Chap. 3, Sec. 4 says:
Cleaning. Acrylic windshields and windows may be cleaned by washing them with mild soap and running water. Rub the surface with your bare hands in a stream of water. Follow with the same procedure but with soap and water. After the soap and dirt have been flushed away, dry the surface with a soft, clean cloth or tissue and polish it with a windshield cleaner especially approved for use on aircraft transparent plastics. These cleaners may be purchased through aircraft supply houses.