Polyvinyl chloride (PVC) is a widely used thermoplastic, but it is inherently thermally unstable. When exposed to heat during processing or service, PVC undergoes dehydrochlorination, leading to the formation of conjugated polyene sequences, discoloration, and loss of mechanical properties. PVC heat stabilizers are vital for stopping this thermal degradation—they work alongside heat to safeguard the polymer’s structure.

PVC heat stabilizers primarily act on heat-caused degradation products to prevent further damage. They work in three main ways: neutralizing the released hydrogen chloride (HCl) to avoid autocatalytic degradation, replacing unstable chlorine atoms in PVC molecules with more stable groups, and trapping free radicals from thermal oxidation. These steps stop the "zipper-like" degradation caused by heat.

Various stabilizers suit different heat conditions. For instance, calcium-zinc stabilizers—an eco-friendly choice—work well in moderate heat, while organotin stabilizers perform best in high-heat processing and offer good transparency. Without heat stabilizers, PVC would break down quickly at processing temperatures (160-200°C), making it unfit for use. Essentially, PVC heat stabilizers work with heat to make the polymer last longer and expand its uses.