Countless number and types of additives are known,  with at least a hundred in each chemical class.   Antioxidants, UV Absorbers, Hindered Amine light stabilizers, flame retardants, internal lubricants, mold releases, impact modifiers,  and anti-stats are just a few of the additives that interact in a polymer matrix.  Picking the wrong combination can lead to catastrophic product failure.  Conversely,  selecting the right combination unlocks synergistic effects and can show significant performance improvement.

Another consideration often overlooked is proper dispersion and product form which can increase cycle times, lower energy costs, and magnify the synergistic effects.