Buyers compare filament by price per kilogram. That number decides almost nothing. What decides your margin is cost per acceptable part — and it moves in the opposite direction to spool price more often than people expect.
The formula
Cost per part ≈ (part mass in grams ÷ 1000) × (price per kg ÷ yield) + machine time + post-processing + scrap
The variables that actually swing the answer:
- Density — a denser polymer needs more grams for the same volume.
- Yield — the share of prints that come out acceptable. This is where cheap filament loses.
- Machine time — a material that prints slower costs more per part even if it is cheaper per kilogram.
- Post-processing — sanding, vapour smoothing, annealing, support removal.
Density comparison
| Material | Density (g/cm³) | ≈ meters per 1 kg at 1.75 mm |
|---|---|---|
| PLA | 1.24 | ≈ 335 m |
| PLA+ | 1.25 | ≈ 333 m |
| PETG | 1.27 | ≈ 327 m |
| ABS | 1.04 | ≈ 400 m |
| ASA | 1.07 | ≈ 389 m |
| PA (Nylon) | 1.14 | ≈ 365 m |
| PA-CF | 1.21 | ≈ 344 m |
| PC | 1.20 | ≈ 346 m |
| TPU 95A | 1.21 | ≈ 344 m |
ABS looks economical here because it is the least dense of the common grades: a given part uses roughly 16% fewer grams than the same part in PLA. That partially offsets its lower spool price advantage — or your disadvantage.
Where yield changes the ranking
- Cheap PLA with diameter drift causes clogs and failed long prints. At a 10% failure rate on a 12-hour print, the "saving" evaporates.
- Wet nylon prints with bubbles and weak layer adhesion. Drying discipline costs time; ignoring it costs parts.
- Engineering grades often allow thinner walls or less infill for the same strength, so the part uses fewer grams of a more expensive material and ends up cheaper.
A worked example
A bracket uses 60 g in PLA. In PA-CF it can be printed at 70% of the mass and still be stiffer, so 42 g. Even at a materially higher price per kilogram, the PA-CF part can win once you include the lower failure rate on a long print and the fact that it survives the application. Run your own numbers with the length and cost calculator.
What to ask your supplier
- Measured diameter distribution for the grade — variation drives failure rate.
- Moisture content and packaging, particularly for nylon and PC.
- Batch color stability if the part is visible.
- Volume pricing tiers, so you can model at your real consumption — see the price list.
Frequently asked questions
Is the cheapest filament always the lowest cost per part?
No. Yield dominates. A cheap spool with diameter variation that causes failed long prints costs more per acceptable part than a consistent spool at a higher price per kilogram.
Why does ABS use fewer grams than PLA for the same part?
Because ABS is less dense — about 1.04 g/cm³ versus 1.24 for PLA. For an identical volume, the ABS part needs roughly 16% fewer grams of material.
When is an engineering filament cheaper than PLA?
When it lets you reduce wall thickness or infill while still meeting the requirement, or when it survives an application that PLA cannot. Fewer grams of a pricier material can beat more grams of a cheap one.