Topcoat clears are simply clears that are intended to be the final or "top" coat of paint applied in a base clear finishing process. As the final coat performance factors such as gloss, depth of image, flow and leveling, ease of polishing, resistance to scratching, hardness, and longevity are some of the key factors a topcoat clear must exhibit to be truly effective. While there have been many attempts from other chemical types there is really only one relevant chemistry for a topcoat clear and that is 2K polyurethane clears. I know some people would argue 2K urethane finishes are different but from a chemical standpoint a 2K urethane actually does not exist rather they all belong in the same "poly" (meaning many) urethane family. Lacquer clear is another type of topcoat clear that has been used in the industry but its relatively ineffectiveness compared to 2K polyurethane clears makes lacquer clear irrelevant for our discussions. While 2K polyurethane chemistry may be the only relevant category for topcoat clears there are variations within the chemistry and "sales hype" which we will discuss in more detail below.
2K Polyurethane MS Clears
MS referes to "Medium Solids" with solids essentially being the amount of film left behind after the solvent evaporates from the applied paint. This represents a wide category of clearcoats encompassing most of the clearcoats available for sale in North America. A simple"MS" description is actually a very broad description so it is difficult to determine much about expectations from this simple description/ If you are investigating a clear that has simply uses "MS" as the description ask the supplier for more detailed information to determine which of the following categories it best fits into.
Turbo, Production, Speed or Spot Clears
You will see these terms used a lot to describe clears that are designed to be polished and put back into service very quickly. These clears are often used by collision repair facilities to improve production through their facilities. These clears often require more polishing to achieve that deep wet look gloss than the next type. However, once polished they can and often do look just as good as Glamour Clears.
Glamour, Overall, Wet Look or Show Car Clears
This class of clear is generally slower in drying than the speed or production clears but this can be good as it allows for more flow and leveling. The down side is that it also make them easier to sag or run and gives more time for dust, bugs and the like to land in the finish. Generally speaking, the "off the gun gloss" (gloss before any buffing) is higher than the faster speed clears. These clears also tend to be less moisture sensitive on drying which can be a benefit to those with less than ideal air delivery systems.
HS or "Higher Solids" Clears will contain more resins and additives which in turn leaves a thicker film left behind after solvent evaporation. This typically results in a deeper, higher gloss finish than "MS" clears. The downsides to this class of clears is that they can be a little harder to spray without orange peel or without sagging or running. Like overall clears, HS clears tend to dry a little slower. Because of the higher solids content JS clears are generally the most expensive variety of clear as well.