pupman.com wrote ...

axwell (now General Atomics Energy Products - mostly uses Mylar (PET), PP, and Polyvinylidene Fluoride (PVDF) film in their plastic cased pulse and energy discharge capacitors. Their very high-energy metal cased (Type C) capacitors use castor oil impregnated Kraft paper, a combination of paper and PP or Mylar film, or PP only as the dielectric. However, these particular capacitors are best suited for rail guns and coin shrinking, not Tesla Coils.

Many of Maxwell's newer pulse capacitors do use self-healing and fusible link metal-film technologies. Unfortunately, many pulse capacitors you'll find on the surplus market tend NOT to use self-healing technology so some care must be used so as not to overvolt them. PVDF is primarily used where higher energy density is required and higher cost can be tolerated. The main application for PVDF capacitors is in defibrillator capacitors and certain specialized/military applications. Most Maxwell caps appearing on eBay tend to be either Mylar of PP.

The best low loss capacitor dielectric for Tesla coil tank circuits is PP film. Although Maxwell doesn't directly indicate which type of dielectric film is used in a given plastic cased capacitor (unless asked), you can usually tell by looking at the specified discharge Repetition Rate (PPS). Capacitors rated at ~1 PPS will be Mylar, while capacitors rated for 1000 PPS will be Polypropylene. Although you can operate a Tesla Coil using Mylar caps, they will heat up and they won't perform as well as PP counterparts.

How do you tell which is which?
Well, Maxwell's older 31XXX series capacitors were mostly 1 PPS Mylar caps, but there are some notable exceptions, such as 31393, 31981, and 31583 (all 1000 PPS). Their series 37XXX caps were mostly 500-1000 PPS, and are therefore PP film.