Most hobby 3D printers use melted plastic but it looks like we can now print using wood! It gets extruded at 200 degrees celsius. If I were to guess I would think it would be a material similar to MDF which is mainly sawdust and glue, of course the glue needs to be one that can be made soft again by reheating.
“A Thingiverse member going by the nom de printer “Kaipa†recently uploaded pictures of 3D-printed parts that weren’t made of extruded plastic, but a wood/plastic mixture he created on his own. The maker wouldn’t share the process for making the material, or even what the ingredients were, but he did offer to send sample spools of his experimental filament to interested hackers.”