Electret materials have been known since the 1920s and were proposed as condenser microphone elements several times, but they were considered impractical until the foil electret type was invented at Bell Laboratories in 1962 by Gerhard Sessler and James West, using a thin metallized Teflon foil.
HMX compositions with teflon-based binders were developed in 1960s and 1970s for gun shells and for lunar seismic experiments.