I use all kind of materials in the handle.

Natural wood, birch bark, stabilized wood, epoxy resin, hybrid with resin and natural materials. Metal, stone, damascus etc.

Sometimes it's my own made or picked up from the forest. I keep my eyes open and try to find something different from the nature, markets, everywhere I go. I do not want to restrict myself to some certain mold. 

Natural wood is good all rounder for many application. The feel is great and somewhat easy to maintain.

Stabilized, epoxy and other artificial materials are good to prevent any damage if the handle get wet, for example in the kitchen, outdoors, diving, etc.

With epoxy and stabilization, I can turn many materials into a usable form for handle material that was not even considered to be possible.