"Plenum" wire comes with a Low Smoke Zero Halogen (LSZH) jacket that burns but does not produce toxic smoke. The change away from PTFE took place as a result of deaths on board the HMS Sheffield in the Faulklands War. Because of burning PTFE, 17 sailors died from inhalation of toxic smoke. PTFE is heat resistant but when faced with temperature inside a burning ship or building, it inevitably burns creating toxic gases. LSZH is typically irradiated PVC. Heating drives off volatiles that leaves the resulting product more heat resistant.