Liner - Spacer Material
Vulcanized fiber is most commonly used as an electrical insulator inside of electronic devices. It is often referred to as fish paper. It has been adopted by the knife making community as a decorative handle material. It is an exceptionally durable material that is a fibrous paper impregnated with an epoxy material that make is very strong. Knife makers commonly call it spacer or liner material.
Use it in between a full tang handle as a liner and handle scale or as a spacer in a full tang handle. Two uses, two names.
You can stack different colors or in combination with sheets of metal, wood, bone or other material for a layered look. For an extra thick look, stack several sheets of the same color. Sanding or grinding the edges will normally blend the material so the seems disappear and it looks like one very thick pieces.
Tip: Make sure and really scratch and scuff the surface of this material before applying adhesive. I use a fresh 36 grit abrasive and then wipe off any dust. The surface of this material is very slick and adhesives need a good tooth for a strong purchase. It is slightly hygroscopic so when you have it mounted in your handle, seal exposed edges with a thin coat of Cyanoacrylate (Superglue type adhesive). A light coat of thin CA will soak in and seal the edges. It's not required but something you can do if the knife is going to be exposed to a lot of moisture or humidity cycling.