uPVC plastics are well known to be a material that are not easily flammable or combustible. Furthermore, uPVC typically will not burn once the source of heat or flame is removed, hence it will not spread fire easily.
This is due to uPVC having more than 50% chlorine in its composition. Chlorine is one of the few elements that confers good fire properties to polymer (plastic).
Therefore, uPVC plastic material have a natural non-flammability and self-extinguishing ability when the source of heat or flame is removed.