PETG-CF filament, ranked by £/kg

Stiffer, matte, dimensionally stable

Carbon-fibre-filled PETG takes an already useful engineering filament and adds short chopped fibres. The result is significantly stiffer, more dimensionally stable, and far less prone to stringing than plain PETG — the fibres change how the melt behaves, and many people find CF grades easier to print than the unfilled version.

It also comes out with a deep matte, slightly speckled finish that hides layer lines well. For functional parts that will be seen, that is a genuine benefit.

What you give up

Carbon fibre makes parts stiffer, not stronger in every sense: filled filaments are generally more brittle and have lower impact resistance than the unfilled polymer. If a part needs to flex or absorb a knock, plain PETG is the better choice. If it needs to hold its shape under load, CF wins.

You need a hardened nozzle

This is not optional and it is the main hidden cost. Chopped carbon fibre wears brass quickly — sometimes within a single spool. The failure is gradual: the orifice widens, extrusion width drifts, and print quality declines in a way that looks like a calibration problem. Fit hardened steel and leave it there. See hardened versus brass nozzles.

A wider nozzle also helps — 0.4 mm works, but 0.6 mm clogs less. See nozzle sizes explained.

Settings to start from

Nozzle 240–260 °C (usually a little hotter than plain PETG), bed 70–85 °C, cooling moderate. Dry it first: CF grades are just as hygroscopic as the PETG underneath.

Buying notes

Expect a clear premium over plain PETG. Fibre content varies between brands and is rarely stated precisely, so results differ more than the label suggests — if one brand works well for you, stay with it.

How to read this table

The per-kilo column is the only number that compares listings honestly. A spool sold at 40% off can still be poor value, and a multi-spool bundle looks expensive until you divide by its total weight. We count bundles at their full weight, so a 4 × 1 kg pack and a single 1 kg spool sit on the same scale.

Where a listing does not state a usable weight we leave the per-kilo figure blank rather than guessing — a wrong ranking is worse than a missing one.