A flame retardant is a chemical substance that is added to materials during their manufacturing process in order to both reduce the likelihood of the finished product catching fire and slow down combustion.
Source: GreenFacts
Since the term “flame retardant” describes a function and not a chemical class, there is a wide range of different chemicals which are used for this purpose. Often they are applied in combinations. This variety of products is necessary, because the materials and products which are to be rendered fire safe are very different in nature and composition. For example, plastics have a wide range of mechanical and chemical properties and differ in combustion behaviour. Therefore, they need to be matched to the appropriate flame retardants in order to retain key material functionalities.
Source: The European Flame Retardants Association
Flame Retardants: Frequently Asked Questions
Español: Pirorretardante
Français: Retardateur de flamme