The materials of mural paintings and contemporary polychromed sculptures more and more frequently displayed in outdoor public spaces are different from those of traditional art techniques, as they come transferred from industrial fields and from technical applications. The control of the artist on these materials is less pronounced, and the problems which may arise in terms of performance and durability must be properly considered by owners and conservators. A critical survey of the use of synthetic paints in outdoor artworks is outlined in this chapter, and the conservation project on the Keith Haring mural in the town of Pisa is described as an emblematic example of the scientific approach towards public art preservation.