These sheets of vulcanized, colorfast, fiber material were developed as an insulating material for electrical uses. Available in rust, black, red, white and in royal blue. Custom knife makers use them to add color and contrast, behind guards (called spacers) and under handle scales (called liners).
Other materials are used as handle spacers, they can be thick or thin, man-made or natural. Thin sheets of brass or stainless steel, when stacked between layers of colored fiber, can add to the dramatic effect on the handle of a well made knife. The photo below of my Texas Ranger Saddle Bowie, shows the use of other types of spacers. Here I used two different composite gemstones, dark blue lapis lazuli and light blue turquoise; with a one inch section of black Water Buffalo horn to seperate them, they all come together to add color and contrast to this handle of sambar stag crown horn.