Epoxy polysiloxane and acrylic polysiloxane finishes are often referred to as one generic type of coating, namely polysiloxane finishes. But are there differences and are these differences important for their performance? The first polysiloxane topcoats were introduced to the market in the mid 90’s and today polysiloxane finishes are recognized as the most advanced decorative and protective finish coating for steel structures in severely corrosive environments. The reason is that polysiloxane topcoats offer unique properties such as long life expectancy, low maintenance cost, superior weather ability, good corrosion protection, fast dry to handle properties, low VOC content, non-isocyanate regulation compliance and extreme durability. Since the mid 90’s the use of polysiloxane finishes has increased and today they are specified for a wide range of larger steel constructions and the experience with the technology is now built on millions of square meters coated with polysiloxane finishes to protect e.g. off-shore structures, oil terminals, storage tanks, bridges, airports, stadiums, pipes, structural steel, concrete silos etc. Some examples of successful applications are shown on figure 5-10. Today, most leading paint suppliers are able to provide advanced polysiloxane finishes and some suppliers are even able to offer improved 2nd generation polysiloxane finishes. These polysiloxane finishes are either based on epoxy polysiloxane or acrylic polysiloxane chemistry in order to balance and optimize their properties. This paper seeks to explain the chemical and physical differences between the state of art epoxy polysiloxane finishes and the state of art acrylic polysiloxane finishes and to relate these differences to differences in performance. Advices will be given in terms of specifying, applying and using polysiloxane coatings. These advices are based on experience from practice as well as experience from extensive testing carried out by expert R&D centers and independent institutes.