One of the most common questions in engineering teams: ‘What’s the difference between Polyamide and Nylon?’ Short answer – there isn’t one. ‘Nylon’ is a trade name DuPont coined in 1938, and ‘Polyamide’ (PA) is the chemical name for the same family of polymers. The real confusion starts with the sub-types: PA6, PA11, PA12, PA66 – each with a completely different performance profile.
The terminology: Nylon, Polyamide, PA
Professionally, ‘Polyamide’ is the precise term used in engineering plastics, injection molding and SLS 3D printing. ‘Nylon’ is mostly reserved for the textile industry and fibers. When an engineer asks for a ‘nylon part’ they usually mean an engineering polyamide – typically PA6 or PA66 for injection molding, or PA12 for SLS/MJF printing.
The main sub-types
PA6 and PA66 – the injection molding standard
PA6 and PA66 are the most common polyamides in injection molding. High mechanical strength, good wear resistance and relatively low cost. The main issue: high moisture absorption (up to 9% by weight) that significantly changes dimensions and mechanical performance. Requires careful drying before processing and environmental conditioning after production.
PA12 – the SLS and MJF king
PA12 is the most common polyamide in SLS and MJF printing. A long carbon chain (12 atoms) that gives significantly lower moisture absorption (under 1.5%), excellent dimensional stability and good chemical resistance. The relatively low melting point suits SLS processes, and it has higher flexibility than PA6 – ideal for functional parts, snap-fits and living hinges.
PA11 – bio-based from castor oil, more sustainable
PA11 is made from castor oil and is considered a bio-based material. Properties very similar to PA12 – low moisture absorption, good dimensional stability – but with better impact resistance and improved UV stability. Drawback: significantly higher cost (1.5-2x PA12) and limited availability from SLS suppliers.
Quick comparison table
- Moisture absorption: PA6 ≈ 9% · PA66 ≈ 7% · PA11 < 2% · PA12 < 1.5%
- Tensile strength: PA66 ≈ 80MPa · PA6 ≈ 70MPa · PA12 ≈ 48MPa · PA11 ≈ 45MPa
- Elongation at break: PA12 ≈ 20% · PA11 ≈ 50% · PA6 ≈ 50% · PA66 ≈ 30%
- Continuous service temp: PA66 ≈ 120°C · PA6 ≈ 100°C · PA12 ≈ 80°C · PA11 ≈ 80°C
- Suitable for SLS/MJF: PA12 ✓✓ · PA11 ✓ · PA6/66 ✗
- Relative cost: PA6 (cheap) < PA66 < PA12 < PA11 (expensive)
PA12 in SLS printing – why this one?
The SLS process requires powder with consistent particle size (40-60 microns), a clear melting point and excellent flow when melted. PA12 meets all these criteria at a reasonable cost. It also allows re-use of unfused powder (typically 50:50 fresh-to-recycled), which dramatically reduces per-part cost.
In MJF the process is similar but with a specific fusing agent jetted at the required points. PA12 in MJF tends to produce parts with higher density, lower porosity and smoother surface finish than classic SLS.
When to choose each
- Injection molding in series of thousands, high mechanical loads → PA66
- Low-cost injection molding, general applications → PA6
- Functional prototypes or end-use parts in SLS/MJF → PA12
- Bio-based application, prolonged UV exposure, high impact → PA11
- Part with continuous wet or submerged exposure → not polyamide, prefer PEEK or POM
Common pitfalls
First pitfall: ignoring moisture absorption. A PA6 part that passed QA dry and within tolerance will swell 0.5% after two weeks in 60% RH air – enough to ruin a precision assembly. Second pitfall: using ‘generic’ PA12 when the application needs a specific additive (Glass-Filled, Carbon-Filled, or PA12-FR for flame resistance). Third pitfall: relying on injection-molded PA12 datasheets when the part is SLS-printed – performance can differ by 30% or more.
Summary
Polyamide and Nylon are the same family – the real debate is between sub-types. For low-cost industrial injection molding: PA6 or PA66. For functional printed parts: PA12 is the no-brainer default. If UV resistance, high impact or a bio-based declaration is needed: PA11. At P3 we print thousands of PA12 parts per month and pick material together with the customer as part of the DfAM process, not after.