Aluminium Polychloride is a straw-yellow solution characterised by remarkable stability, even though its alumina content is over twice that of aluminium sulphate (alum) solutions.

Aluminium Polychloride compounds are polymeric compounds of aluminium hydroxides at various levels of chloride content; They are designated by this generic formula: (Aln(OH)mCl3n-m) x. These compounds contain long chains of atoms and therefore have a higher molecular weight and a larger (positive) electrical charge. This implies that upon hydrolysis they generate aluminium polyhydroxides, which also have long molecular chains of larger dimensions and high weight. These properties make Aluminium Polychloride extremely useful in some processes such as papermaking and water clarification