Not Real Metal — But Close Enough to Fool People
By Inno Uncle
Metal-filled filaments are PLA or PETG loaded with 30-60% fine metal powder — usually bronze, copper, stainless steel, or iron. The prints come off the bed looking like dull ceramic, but with the right post-processing they develop a genuine metallic sheen and heft that standard filament can't match.
Printing: What You Need to Know
Metal-filled filament is abrasive. A standard brass nozzle will be destroyed within a single kilogram. You need a hardened steel or ruby-tipped nozzle — 0.6mm or larger is strongly recommended. Smaller nozzles clog constantly with these materials.
Print temperature is typically 10-15°C higher than standard PLA. Slow down to 30-40mm/s. The metal powder makes the filament more brittle, so avoid tight bends in your filament path. A dry box is essential — metal-filled PLA absorbs moisture even faster than regular PLA.
Post-Processing: From Dull to Stunning
This is where the magic happens. Start with wet sanding: 400 → 800 → 1200 → 2000 grit. The metal particles get exposed as you remove the plastic surface layer. For bronze and copper fills, follow up with steel wool (0000 grade) and then metal polish (Brasso works great). The result is a warm, genuine metallic luster.
For iron-filled filament, you have an extra trick: rusting. Spray with a salt-vinegar solution and let it sit overnight. You'll get a genuine rust patina that's perfect for decorative or cosplay pieces. Seal with clear coat to stop the process.
Steel-filled prints can also be cold-blued using gun bluing solution. The result is a dark, industrial finish that looks nothing like plastic.
After polishing, protect the finish with a thin coat of clear lacquer or Renaissance wax. The metal particles can oxidize over time without a sealant.
If you're looking for build surfaces that handle these materials well, check our PEI build plates — the textured surface gives excellent adhesion for metal-filled filaments.