Carbon vs Glass Fibre Filament, Compared

What chopped fibre actually does to a printed part, when carbon beats glass, which polymer to put it in — and why you need a hardened nozzle first.

Chopped fibre turns an ordinary engineering plastic into something that holds its shape under load and heat. It also eats nozzles, needs drying, and costs several times what a spool of PLA does. Here is how to pick one, and when not to.

What the fibre actually does

A few percent of chopped carbon or glass fibre, milled to well under a millimetre, does four things to a printed part:

Stiffness goes up sharply. This is the headline. A CF-filled nylon is dramatically less bendy than the same nylon unfilled.
Warping goes down. The fibres restrain shrinkage as the part cools, which is why filled nylons print flatter than neat ones.
Heat deflection goes up. The part holds its geometry closer to the polymer's real temperature limit.
Elongation goes down. This is the cost. Filled parts are stiffer but less forgiving — they crack rather than bend.

That last point is the one people miss. Fibre reinforcement is not "the same part but stronger". It is a trade: you buy stiffness and dimensional stability with toughness.

Carbon or glass?

They are not competitors so much as different answers.

Carbon fibre is stiffer per gram, holds tighter tolerances, and is what you want when deflection under load is the thing you are fighting. It is black, always. It is also mildly electrically conductive, which matters more often than people expect — a CF part is not an insulator, and it has no business as a battery holder or a terminal cover.

Glass fibre is cheaper, less stiff, and noticeably tougher — it tolerates an impact that would crack the carbon-filled equivalent. It is not conductive. It is usually a light grey or natural colour, so it takes dye and paint better.

Rough rule: carbon for stiffness, glass for toughness and for anything near electricity.

Then pick the polymer under it

The fibre is the smaller half of the decision. What the fibre is mixed into decides heat, chemical resistance, and how difficult your evening is going to be.

Nylon (PA6, PA612, PA12)

The workhorses. Tough, good fatigue life, good wear behaviour — the right answer for gears, bushings, clips and living hinges that also need stiffness.

Nylons are hygroscopic, and it is not a mild effect: a nylon spool left out overnight will print with visible steam, poor layer bonding and a rough surface. Dry it, and print it out of a dry box.

PA6-CF20 is the stiff, strong one — and the thirstiest.
PA612-CF15 absorbs markedly less moisture and stays dimensionally stable, which makes it the easier of the two to live with.
PA12-CF10 is the most stable and the least thirsty again, at some cost in stiffness.

PET (PET-CF, PET-GF)

The sensible middle. Much less moisture-sensitive than nylon, good stiffness, good heat resistance, and far more forgiving to print. If you are reaching for a fibre-filled material for the first time, a PET-CF is where to start.

PETG-rCF and the ESD grades

PETG with recycled carbon is the entry point — the easiest to print of anything here and the cheapest way to find out whether filled filament solves your problem.

The ESD grades exist for a specific job: handling electronics. They are formulated to bleed static away in a controlled fashion rather than insulate it or short it. If you are printing trays, jigs or fixtures that touch circuit boards, this is the reason they exist.

PPS

The specialist. Outstanding chemical resistance and the highest continuous service temperature of anything on this list. It is also the hardest to print and the most expensive by a wide margin. Reach for PPS when a part has to survive solvents or sustained heat that would soften everything above it — and not before.

Polymaker's Fiberon range documents the individual grades in more detail than a shop listing sensibly can.

What printing these actually requires

Be honest with yourself about the printer before ordering:

A hardened nozzle. Not optional. Chopped fibre is an abrasive. It will ream a brass nozzle out of round in a few hundred grams and your dimensions will drift long before you work out why. Hardened steel is the minimum; ruby or tungsten carbide if you print a lot.
A dryer, for the nylons. Not a nice-to-have.
Hot end temperature well above the PLA range, and for the higher grades an all-metal hot end and a heated chamber.
Patience with first layers. Filled materials are less tacky.

If any of that is a problem, that is a completely reasonable reason to have someone else print the part.

What we stock, and what it costs

We carry Polymaker's Fiberon range in 0.5 kg, 1 kg and 3 kg spools — 28 listings, because each grade and spool size is priced separately rather than hidden behind one dropdown:

Grade	Fibre	Good for
PETG-rCF08	Recycled carbon	The easy first step
PET-CF17	Carbon	Stiff, stable, forgiving
PET-GF15	Glass	Tough, non-conductive, comes in colours
PA6-CF20	Carbon	Maximum stiffness in a nylon
PA612-CF15	Carbon	Nylon that tolerates humidity
PA12-CF10	Carbon	The most dimensionally stable nylon
PA6-GF25	Glass	Tough, impact-tolerant nylon
PETG-ESD, PA612-ESD	—	Static-dissipative, for electronics work
PPS-CF10, PPS-GF20	Carbon / glass	Chemicals and sustained heat

Prices run from $23.99 for a 0.5 kg spool up to $335.99 for 3 kg of PPS-GF20 — a spread that tells you exactly how far apart the ends of this range are.

Or have us print it

Fibre-filled parts are a good candidate for outsourcing, precisely because the equipment cost is real. Upload your model for an instant quote and pick the material — the price comes from a real slicer run against the machine that will make it.

Frequently asked

Will carbon fibre filament make my part as strong as carbon fibre? No, and the naming does the industry no favours. Chopped fibre in a printed part is not continuous-fibre laminate. It raises stiffness substantially; it does not approach the strength of a layup.

Do I really need a hardened nozzle? Yes. This is the single most common expensive mistake with these materials.

Which one should I try first? PETG-rCF08 or PET-CF17. Both print close to ordinary PETG and neither will punish a slightly damp spool.

Is CF filament conductive enough to matter? It is not a wire, but it is not an insulator either. Do not use it where insulation is the part's job.

Why is PPS so expensive? The base polymer costs many times what nylon does. You are paying for the chemistry, not the fibre.