Key takeaways
- Substituting upward in performance is nearly always mechanically safe, and nearly always harder to print.
- Check in order: heat, load type, environment, printer capability. Skipping the first filter breaks parts.
- Changing material means changing the whole profile. Reusing the old one is the fastest way to blame the wrong thing.
- Price per kilogram is rarely the real cost difference — failure rate and machine hours are where the money goes.
The question always arrives at the worst moment: a job is running, the grade it calls for is out, and there are three other spools on the shelf. This is the process we use in the Studio to answer it in minutes instead of hours.
Four filters, in this order
- Peak service temperature. The substitute must match or beat the heat deflection figure. This is the one filter with no negotiation, because heat failures are quiet — the part sags rather than snapping.
- Load type. Static load wants modulus. Impact load wants elongation and impact energy. A material with higher tensile strength but lower elongation is not an upgrade for a part that gets dropped.
- Environment. Direct sun, water, oils, chemicals, food contact. This filter eliminates more candidates than people expect, and it is where PLA loses almost every outdoor argument.
- Your printer. Enclosure, maximum nozzle temperature, hardened nozzle, dry box, ventilation. A material your machine cannot run is not a substitute, however good the data sheet looks.
The substitution table
| Wanted | Substitute with | Trade-off |
|---|---|---|
| PLA | PETG → PLA High Speed → ABS | PETG prints slower and needs drying; slightly less crisp surface detail |
| PLA High Speed | PLA Matte → PLA-CF | Noticeably longer print times; PLA-CF needs a hardened nozzle |
| PETG | ASA → ABS → PA12 | All three need an enclosure; ABS and ASA need ventilation |
| ABS | ASA → PC Blend → PETG-CF | ASA costs noticeably more; PETG-CF stops around 69 °C HDT, so recheck the heat filter |
| ASA (outdoors) | ABS with a UV topcoat → PC Core | Bare ABS chalks and surface cracks within months of sun; a coating is recurring maintenance |
| TPU 95A | TPU 85A printed slower → PA12 | 85A is much softer and prints three times slower; PA12 is tough but not elastic |
| TPU 85A | TPU 95A with thinner walls | No substitute for surface feel; only for the elastic function, and only if you redesign |
| PA-CF | PA6-GF → PC Core → PETG-CF | PA6-GF is heavier and harder on nozzles; PETG-CF gives up 60 °C of heat resistance |
| PA12 | TPU 95A → PETG → PC Core | Nothing replaces the ductility of unfilled nylon at the same stiffness — and almost nobody publishes a number for it |
| PC Core | PC Blend → ABS → PA-CF | Alloyed PC keeps the heat (112 °C against 111 °C for PolyLite PC) and is far tougher notched — 25.8 against 4.1 kJ/m² |
| Tough resin | Model resin with thicker walls | Still brittle; snap fits and threads will break during assembly |
Three swaps that nearly always work
One-way, low risk
- ABS → ASA
- Same settings, same mechanicals, plus UV stability. It only costs more.
- PLA → PETG
- 17 °C more heat, twice the impact energy, water resistance. Costs speed and drying.
- PA-CF → PA6-GF
- 43 °C more heat and more stiffness. Costs weight and nozzle life.
Note that all three hold in one direction only. ASA substitutes for ABS, but if the part has to be acetone welded into a single piece, ABS is the one that does that well. PETG substitutes for PLA, but for a design review model that needs sharp edges and a flat surface, matte PLA still wins.
Four substitutions that look sensible and are not
- PLA-CF instead of PETG for a load-bearing part. The words "carbon fibre" read like an upgrade. The numbers do not: Polymaker publishes 31.2 MPa and 54 °C HDT for PLA-CF against 50.8 MPa and 78 °C for PolyLite PETG. It is a downgrade on both of the filters that matter more.
- ABS instead of PETG for an outdoor housing. ABS does handle more heat, but it is the least UV-stable material in the engineering set. After one sunny season the surface crazes and the part turns brittle.
- PETG instead of TPU for a gasket. PETG bends, but it does not return. A compressed PETG gasket stays compressed and stops sealing.
- Model resin instead of tough resin for threaded parts. Thicker walls do not fix brittleness. The thread strips on the second time it is tightened.
Relative cost index
The table below indexes cost per kilogram with matte PLA at 1.0×. Use it to rank options while weighing a substitution, not as a quote — actual prices per grade and per weight are quoted on request.
| Material | Index | Material | Index |
|---|---|---|---|
| PLA High Speed | ≈ 0.9× | TPU 95A | ≈ 2.0× |
| PLA Matte | 1.0× | PC Blend | ≈ 1.9× |
| ABS Core | ≈ 1.05× | PC Core | ≈ 2.4× |
| PETG Core | ≈ 1.1× | PA12 | ≈ 2.3× |
| ASA Core | ≈ 1.3× | PA6-GF | ≈ 2.6× |
| PLA-CF | ≈ 1.4× | PA-CF | ≈ 2.8× |
| PETG-CF | ≈ 1.6× | TPU 85A | ≈ 3.5× |
A 1.3× difference in spool price can be a 2× difference in part cost once failure rate and machine hours are counted.
This is why comparing by price per kilogram nearly always leads to the wrong decision. A spool of ASA runs about 20 % over PETG, but it also needs an enclosure, prints slower, and fails more often on large parts — the real gap in part cost is much wider. In the other direction, if one PA-CF part replaces three machined aluminium ones, a 2.8× index is simply not the relevant number.
After the swap, swap the settings too
The most common mistake in a material change is not picking the wrong grade — it is printing the new grade on the old profile. Three things have to be retuned every time:
- Temperature and cooling. Every 10 °C at the nozzle visibly changes layer adhesion. PLA's 100 % fan will crack ABS apart at the layer lines.
- Flow and shrinkage. Amorphous grades (PLA, PETG, ABS) shrink little; crystalline nylon shrinks considerably more and then swells as it takes up moisture. Any part that has to fit needs a fresh tolerance test after a material change — your own spool's number beats any table.
- Drying. If the new grade is more hygroscopic than the old one, drying stops being optional. Per-grade schedules are in the drying guide.
If you are starting from scratch rather than substituting, the material finder walks the same four filters, and every Material Passport publishes the same fields so you compare like with like.
Frequently asked
Can PETG replace PLA?
Yes, in most cases. On Polymaker's data sheets PETG reaches 76–78 °C HDT against 53–60 °C for PLA, and it ignores water. You accept slower printing, a drying step, and slightly less crisp surface detail. The reverse does not hold: PLA cannot replace PETG in anything that runs warm or gets dropped.
Are ASA and ABS interchangeable?
ASA substitutes for ABS almost completely — the same settings group, equal or slightly better mechanicals, plus UV stability. The reverse only holds indoors. For an outdoor part, ABS will chalk and surface crack within months of sun exposure.
What replaces PA-CF if my printer has no enclosure?
Honestly, nothing does. PETG-CF is the closest grade that runs on an open frame, but Polymaker publishes 68.6 °C HDT for Fiberon PETG-rCF08 against 215 °C for PA6-CF20 — nearly 150 °C apart. If the part genuinely needs PA-CF performance, outsource the print rather than downgrade the material.
Is comparing filament by price per kilogram accurate?
Not on its own. Spool price is typically only 30–50 % of part cost. Harder materials bring higher failure rates, longer machine hours and more post-processing, so the real gap in part cost is usually wider than the gap in spool price.
Do I need to reprint tolerance tests after changing material?
Yes, for anything that has to fit. Shrinkage varies significantly between families — amorphous grades shrink little, crystalline nylon a good deal more — so a hole that fits in PLA will not fit in PA12. Reprint a hole and fit gauge before committing a batch.