Hello Craig, I have experience with both Howe Fill and Howe Film from approximately 2-3 years ago. I had a metal core board of .060 thick CIC and used the Fill successfully in low volume production. The Film product was used in some quantity of prototype. They are both Polyimide resin with ceramic particles, the Film has a cloth structure (i.e., Polyimide or FR4) where the Fill has none. The Fill is literally sprinkled onto the surface. Both products allowed two multilayer subs to be laminated without additional CIC core hole fill processing. Both products -like all the Arlon materials- are excellent. The Film is widely used for the CIC foil (thickness of <.010) while the fill is used on the thicker cores. The construction is expensive and the two materials and associated processes are (appropriate) adders. Thermount material has put a huge dent in the metal constraining core product and the future existence of the Howe Film and Fill, as well as metal cores such as CIC is in question. I will say that the HoweFill succeeded where other materials failed. The name "Howe" is derived from a most excellent fellow whom unfortunately was lost in an automobile accident. Art Howe did much for PWB industry and excelled in the Polyimides. Feel free to give me a buzz; 781 858 0783... [log in to unmask] Best regards, Coretec Brad