| Polyamide (PA/Nylon) and polyester (PET/PBT/PETG) are the two largest families of engineering thermoplastics in injection molding. PA is preferred where self-lubrication, fatigue resistance, and toughness under mechanical load are required. Polyester, specifically PBT, is preferred where low moisture absorption, dimensional stability in humid environments, and electrical insulation properties are the priority. Both families include glass-fiber-reinforced grades that extend performance to 200–250°C service temperatures. |
Both material families appear across automotive, electronics, industrial, and consumer product applications. The choice between them is rarely obvious from brand names or generic descriptions — it depends on specific processing conditions, the service environment, and dimensional requirements that generic comparisons rarely quantify.
This guide compares both materials on the properties that matter for engineering design and injection molding: mechanical data, processing parameters, moisture sensitivity, chemical resistance, and the application scenarios where each material wins.
What Are Polyamide and Polyester?
Polyamide (PA) — The Nylon Family
Polyamide is the engineering name for the polymer family commonly called nylon. Polyamides are formed by condensation polymerization — the reaction of diamine and dicarboxylic acid monomers creates amide bonds (–CO–NH–) that link the polymer chains. The number designation (PA6, PA66, PA12) refers to the number of carbon atoms in the monomers or the chain segment between amide groups.
The amide bond gives polyamide its characteristic combination of high toughness, low friction coefficient (0.15–0.35 against steel), and reasonable heat resistance. It also makes PA hydrophilic — the amide groups attract and hold water molecules, which plasticizes the polymer. This moisture absorption is the defining processing challenge for PA injection molding.
- PA6: Most economical engineering polyamide. Broad availability, good toughness, Tm = 220°C. Standard for gears, bushings, and general structural components.
- PA66: Higher melting point (260°C) and stiffness than PA6. Better fatigue resistance and heat stability. The standard for automotive and connector applications requiring continuous service above 100°C.
- PA12: Lowest moisture absorption of the common polyamides (0.25% at equilibrium). Best dimensional stability in wet environments. Used in medical tubing, fuel line components, and flexible packaging.
- PA66-GF30: PA66 reinforced with 30% glass fibre. HDT increases to 240–250°C; tensile strength to 180–200 MPa. The standard metal-replacement material for high-load structural applications.
Polyester (PET / PBT / PETG) — The Ester Family
Polyesters are formed by condensation of diacids with diols — the ester linkage (–CO–O–) gives the polymer family its name. PET (polyethylene terephthalate), PBT (polybutylene terephthalate), and PETG (glycol-modified PET) are the three grades with significant injection moulding application.
- PBT: The workhorse polyester for injection molding. Low moisture absorption (0.07%), excellent dimensional stability, and a processing-friendly nature make it the #1 choice for connector housings and electronic enclosures. Tm = 225–235°C.
- PET: Higher stiffness and better barrier properties than PBT. More sensitive to moisture during processing — requires pre-drying to < 0.02% moisture at 150°C. Used in high-strength structural applications and medical packaging.
- PETG: Glycol modification prevents crystallization during cooling — making PETG amorphous, transparent, and easier to process than standard PET. Excellent optical clarity for transparent housings, medical packaging, and display components. Lower shrinkage (0.3–0.5%) than crystalline PBT or PET.
Polyamide vs Polyester: Full Engineering Comparison
The table below covers all engineering-relevant properties for both material families in their injection-molded form. Data applies to the most common injection molding grades unless otherwise noted.
| Eigenschaft | Polyamid (PA / Nylon) | Polyester (PET / PBT / PETG) |
| Zugfestigkeit (ungefüllt) | PA6: 70–80 MPa PA66: 80–85 MPa | PET: 55–75 MPa PBT: 50–60 MPa PETG: 45–55 MPa |
| Biegemodul | PA6: 2.5–3.0 GPa PA66: 2.8–3.3 GPa (glass-filled PA66-GF30: 9–11 GPa) | PBT: 2.0–2.8 GPa PET: 2.8–4.2 GPa (PBT-GF30: 9–10 GPa) |
| Schmelzpunkt | PA6: 220°C PA66: 260°C PA46: 290°C | PET: 255–260°C PBT: 225–235°C PETG: 220–225°C |
| Wärmeformbeständigkeitstemperatur (1.82 MPa) | PA6 (dry): 65°C PA66 (dry): 90°C PA66-GF30: 240–250°C | PBT: 55–65°C PBT-GF30: 200–210°C PET-GF30: 220–230°C |
| Water absorption (24h, 23°C) | PA6: 2.7% PA66: 2.5% PA12: 0.25% (lowest) | PBT: 0.07–0.08% (excellent) PET: 0.1–0.2% PETG: 0.1–0.2% |
| Dimensional stability under moisture | Moderate — PA66 swells ~0.5–1.0% at equilibrium moisture content; must account for in precision parts | Excellent — PBT and PET swell < 0.05% in water. PBT preferred for precision connector housings and sensor components |
| Chemische Beständigkeit | Resistant to oils, greases, hydrocarbons; attacked by strong acids and oxidising agents | Excellent resistance to dilute acids, organic solvents, alkalis; fair against strong oxidising agents |
| Selbstschmierung | Excellent — low friction coefficient (µ = 0.15–0.35 vs steel); used dry in gears, bushings, cams | Moderate — lower self-lubrication than PA; often requires PTFE additive in bearing applications |
| UV-Beständigkeit | Poor — PA6 and PA66 degrade under prolonged UV; requires UV stabiliser additive | Good — PET has inherently better UV stability than PA. Outdoor applications favour PET or UV-stabilised PBT |
| Shrinkage (unfilled) | PA6: 0.6–1.4% PA66: 0.8–1.5% | PBT: 1.5–2.5% PET: 1.5–2.5% PETG: 0.3–0.5% (lowest) |
Key Property Differences in Depth
Moisture Absorption — The Critical Practical Difference
PA66 absorbs 2.5% water at equilibrium (23°C, 50% RH). PA6 absorbs 2.7%. This moisture is not merely a surface effect — it penetrates throughout the polymer matrix, acting as a plasticiser. The absorbed water reduces tensile strength and stiffness, but improves impact toughness and elongation. The net dimensional change is 0.5–1.0% in each linear dimension — far exceeding the tolerance budget of most precision components.
PBT absorbs 0.07% moisture — an order of magnitude less than PA66. For applications where dimensional precision across varying humidity conditions is required — connector housings, bearing cages, sensor enclosures — PBT provides practical immunity to this effect. PA12 is the exception in the PA family: its 0.25% moisture absorption approaches PBT and makes it the preferred polyamide for humidity-sensitive precision applications.
Mechanische Festigkeit und Ermüdungsverhalten
PA66 in dry-as-molded condition outperforms PBT in tensile strength. The comparison at equilibrium moisture is more nuanced: absorbed moisture reduces PA66 tensile strength, while improving impact resistance. This moisture-conditioned state is the one relevant to most service conditions.
Fatigue resistance — resistance to failure under repeated cyclic loading — strongly favors PA over PBT. PA’s self-lubrication and energy-absorbing molecular structure make it the material of choice for gears, cams, and bearing applications subject to millions of loading cycles.
Adding 30% glass fiber to PA66 improves fatigue resistance by 2.5× versus the unfilled grade — a performance advantage confirmed across DuPont Zytel® GF grade test data and referenced in the ISO 16396 classification framework for polyamide molding materials. [3].
Heat Resistance and Glass-Fiber Reinforcement
Unfilled PA6 and PBT have similar heat deflection temperatures at 1.82 MPa load — both insufficient for continuous elevated-temperature service. The picture changes dramatically with glass fibre reinforcement.
PA66-GF30 achieves HDT of 240–250°C — sufficient for automotive under-hood applications. PBT-GF30 achieves HDT of 200–210°C. Both are vastly superior to their unfilled equivalents and represent the practical choice for high-temperature structural components in either material family.
Chemische Resistenz
Both materials resist oils, greases, dilute acids, and common organic solvents. The critical difference: PA resists oils and hydrocarbons better — making it the standard choice for fuel system components, oil-bath gearbox parts, and under-hood automotive applications. PBT resists dilute acids and alkaline cleaning agents better, but is attacked by strong alkalis and hot water above 60°C without hydrolysis stabiliser additives.
Automotive fuel line connectors use PA12 for its combination of fuel resistance, low moisture absorption, and flexibility. Electronic connector housings use PBT for its combination of electrical insulation, dimensional stability, and resistance to the acidic flux residues used in PCB soldering operations.
Injection Molding Polyamide (PA/Nylon): Processing Guide
PA injection molding is well-established across automotive, industrial, and consumer electronics applications. The process is forgiving in terms of processing window, but moisture management before and during molding is critical and non-negotiable.
| Parameter | PA Specification | Technische Hinweise |
| Vortrocknen | 80°C for 4–8 h (PA6); 80°C for 3–4 h (PA66) — to < 0.2% moisture | Moisture in PA causes splay, surface defects, and reduced molecular weight. Never skip drying. Desiccant hopper dryer preferred over hot-air dryer. |
| Barrel temp | PA6: 230–260°C PA66: 260–290°C PA12: 200–230°C | Keep melt time short — PA degrades at elevated temperatures. Purge with PP or PE before long shutdowns to prevent black specks from degraded PA. |
| Mould temp | PA6: 60–90°C PA66: 80–100°C | Higher mould temperatures increase crystallinity, improving dimensional stability and fatigue resistance at the cost of cycle time. For structural gear applications, use the higher end of the range. |
| Einspritzdruck | 600–1,200 bar (hold: 50–80% of fill pressure) | PA has low melt viscosity — excessive pressure causes flash. Use anti-drool (self-locking) nozzles to prevent drool between shots. Control hold pressure precisely to avoid overpacking thin walls. |
| Schrumpfungskompensation | PA6: 0.6–1.4% PA66: 0.8–1.5% (GF grades: 0.3–0.7%) | Anisotropic shrinkage in glass-filled grades — shrinkage perpendicular to flow direction is higher than parallel. Must simulate with Moldex3D or Moldflow before cutting steel for precision parts. |
| Gate sizing | Minimum 0.8 mm diameter for unfilled PA | PA’s low viscosity allows small gates — but undersized gates cause excessive shear and material degradation. Submarine and pin-point gates work well for PA. Hot runners reduce runner waste significantly. |
| Post-molding conditioning | Optional: 70°C/water soak (2–4 h) to pre-condition parts | PA parts are dry and brittle immediately after molding. Moisture conditioning to 50% RH equilibrium restores toughness. Critical for parts going directly into assembly without field conditioning. |
Glass-fibre reinforcement changes the processing equation for PA: adding 30% glass fibre to PA66 increases tensile strength from ~85 MPa to 180–200 MPa, and HDT from 90°C to 240–250°C — at the cost of anisotropic shrinkage.
The shrinkage perpendicular to glass fiber orientation is significantly higher than parallel to it, meaning warpage in large flat parts becomes a design and mold engineering problem that must be solved with simulation before tooling is cut.
Per BASF’s Ultramid processing guide, pre-drying to ≤ 0.15% moisture at 80–100°C for 4 h is required before moulding GF-reinforced PA66 grades. [1].
→ See Fecision’s PA/Nylon injection molding capabilities: fecision.com/materials/nylon-injection-molding/
Injection Molding Polyester (PET / PBT / PETG): Processing Guide
Polyester injection molding requires more careful moisture management than PA — particularly for PET, which undergoes irreversible hydrolytic chain scission if molded with residual moisture above 0.02%. PBT is more forgiving, and PETG is the most process-friendly grade of the family.
| Parameter | PET/PBT/PETG Specification | Technische Hinweise |
| Vortrocknen | PBT: 120°C for 3–4 h PET: 150°C for 4–6 h PETG: 65°C for 3–4 h — to < 0.02% moisture | PET is highly sensitive to hydrolysis — moisture above 0.02% causes irreversible chain scission during molding, reducing molecular weight and producing brittle, structurally weak parts. PETG is more forgiving at lower drying temperatures. |
| Barrel temp | PBT: 230–260°C PET: 265–285°C PETG: 220–250°C | PBT has the widest processing window of the polyester family and is the most forgiving. PET requires tight temperature control — exceeding 290°C for more than 5 minutes initiates acetaldehyde generation and thermal degradation. |
| Formtemperatur | PBT: 40–80°C PET: 80–120°C PETG: 10–30°C (cool for clarity) | Hot mould temperatures for PBT and PET promote crystallisation, improving HDT, chemical resistance, and surface quality. PETG, being amorphous, benefits from cold moulds that maximise optical clarity. |
| Einspritzdruck | 800–1,400 bar (hold: 40–60% of fill pressure) | PET and PBT crystallise rapidly — pack pressure must be applied quickly. Insufficient packing causes sink marks and voids adjacent to thick sections. Gate freeze-off timing is critical for dimensional consistency. |
| Schrumpfungskompensation | PBT: 1.5–2.5% (unfilled) PBT-GF30: 0.3–0.8% PETG: 0.3–0.5% | PBT unfilled exhibits relatively high shrinkage — warpage risk in large flat parts without ribs. GF reinforcement dramatically reduces shrinkage and anisotropy. PETG’s low shrinkage produces dimensionally stable transparent parts. |
| Gate sizing | 0.8–1.5 mm diameter preferred | PBT crystallises quickly at the gate — undersized gates cause premature freeze-off, short shots, and high weld-line intensity. Larger gates also reduce shear-induced orientation in transparent PETG parts. |
| Chemical resistance notes | Excellent to dilute acids, organic solvents, aliphatic hydrocarbons | PBT is attacked by strong alkalis and hot water above 60°C — specify PBT-GF grades or add hydrolysis stabiliser for hot/wet service conditions. PETG resists most cleaning agents used in medical packaging. |
PBT’s rapid crystallisation during cooling is both an advantage and a constraint. Rapid crystallisation gives PBT excellent surface quality and chemical resistance — but it also means that gate freeze-off happens quickly, limiting the pack pressure window.
PETG’s amorphous structure and low drying temperature make it the most approachable polyester grade for transparent part production. Unlike PC, PETG does not require high processing temperatures and has excellent chemical resistance. Its low shrinkage (0.3–0.5%) makes it a reliable choice for dimensionally stable transparent housings and medical packaging components.
DuPont’s Rynite® PBT and PET processing guide confirms that standard PET requires drying to < 0.02% moisture before moulding to prevent hydrolytic chain scission — PETG’s glycol modification lowers this sensitivity, allowing a more forgiving 65°C drying protocol. [2].
→ See Fecision’s PET injection molding capabilities: https://fecision.com/materials/pet-injection-molding/
Applications: Where Each Material Is Used
Polyamide Applications in Engineering
Zahnräder, Lager und Buchsen: PA’s self-lubrication (µ = 0.15–0.35 vs steel) and fatigue resistance make it the standard for dry-running transmission components in printers, power tools, office equipment, and industrial automation.
Automotive under-hood: Air intake manifolds (PA66-GF30), fuel line connectors (PA12), coolant system components, and engine cover clips all exploit PA’s thermal stability and hydrocarbon resistance at continuous temperatures of 100–150°C.
Electrical connectors and cable ties: PA66 provides the mechanical retention force (spring-back after deflection) required for reliable locking clips in wiring harness connectors, and the toughness to survive assembly line handling. Cable ties — the highest-volume PA moulded product globally — demand exactly this combination of stiffness and toughness.
Medical and food-contact flexible components (PA12): PA12’s low moisture absorption, flexibility, and chemical resistance make it the preferred polyamide for medical tubing, catheter components, food packaging films, and pneumatic tubing in processing equipment.
Polyester Applications in Engineering
Connector housings (PBT): PBT is the #1 connector housing resin globally. Its moisture independence (0.07% absorption) means pin-to-pin spacing is stable across climates, and its UL 94 V-0 rated grades meet the flammability requirements of electrical equipment standards.
Electronic enclosures and sensor housings (PBT): Automotive sensors (wheel speed, crankshaft position, mass air flow) use PBT-GF30 housings because PBT’s dimensional stability under underhood conditions is superior to PA — the connector interface must mate reliably at −40°C to 125°C without positional drift from moisture absorption.
Transparent structural components (PETG): Medical packaging trays, point-of-care diagnostic device windows, and consumer product enclosures where clarity and chemical resistance are both required. PETG’s resistance to hospital disinfectants and FDA food-contact compliance make it the preferred transparent engineering polymer for regulated applications.
Packaging and beverage containers (PET): While blow-moulded PET bottles dominate the packaging sector by volume, injection-moulded PET preforms (the precursors to blow-moulded bottles) are produced at hundreds of millions of units annually. Injection-moulded PET packaging trays and containers also serve food and pharmaceutical applications.
Application Selection Guide: Which Material to Choose
The table below maps common engineering requirements to material choice, with the engineering rationale for each recommendation.
| Bewerbungsvoraussetzung | Materialwahl | Technische Begründung |
| Continuous motion / bearing / gear (unlubricated) | Choose PA | PA’s self-lubrication (µ = 0.15–0.35) and fatigue resistance make it the default for dry-running gears, bushings, and cam followers. PA66-GF30 for elevated-load or elevated-temperature versions. |
| Connector housing or electronic enclosure | Choose PBT | PBT’s extremely low moisture absorption (0.07%) maintains dimensional stability in humid environments. PA connectors can change dimensions by 0.5–1.0% from dry-as-moulded to moisture-equilibrated. |
| High operating temperature (> 100°C continuous) | Choose GF grade of both | PA66-GF30: HDT 240–250°C. PBT-GF30: HDT 200–210°C. Plain (unfilled) grades of both are unsuitable above 80–90°C continuous load. |
| Precision dimensional stability in humid environment | Choose PBT or PETG | PBT absorbs < 0.08% moisture — dimensions are essentially independent of humidity. PA in the same environment will have absorbed 2–3% moisture and changed dimensions by 0.3–0.8%. |
| Food contact or medical packaging component | Choose PETG or PA12 | PETG is FDA-compliant, transparent, and resistant to common cleaning agents. PA12 has the lowest moisture absorption of any polyamide (0.25%) and is used in medical tubing and flexible food-contact components. |
| Transparent structural component | Wählen Sie PETG | PBT and PA are opaque in standard grades. PETG provides good optical clarity, impact resistance, and chemical resistance. PC offers better optical clarity but lower chemical resistance. |
| Chemical exposure to oils / hydrocarbons | Choose PA | PA resists oils, greases, and aliphatic hydrocarbons well — making it preferred for automotive under-hood components (fuel line connectors, air intake manifolds) where oil splash is constant. |
| Cost-sensitive high-volume commodity part | Compare PET vs PA6 | Unfilled PET is typically less expensive than PA6 per kilogram at commodity grade. For parts where either material meets the performance specification, PET frequently offers cost advantage. |
| UV-exposed outdoor component | Choose UV-stabilised PBT or PET | Unfilled PA degrades under UV. PBT and PET are inherently more UV-stable; UV-stabilised grades for prolonged outdoor exposure. Both materials are available with carbon black UV absorbers for maximum durability. |
The most common selection mistake: choosing PA for connector housings because it is the better-known engineering polymer, without accounting for dimensional change under humidity cycling. PA66 connector housings in humid environments can shift pin spacing by 0.3–0.5 mm from dry-as-moulded state — exceeding the mating tolerance of fine-pitch connectors. PBT eliminates this problem completely.
Cost, Environmental Impact, and Sustainability
Kostenvergleich
PA6 is the least expensive PA grade and competes favorably with PBTon a per-kilogram basis. However, the correct cost comparison is cost per part — which depends on part weight, cycle time, and scrap rate. PA’s faster crystallization in some molds can reduce cycle time; PBT’s wider processing window can reduce scrap rate.
Commodity PET is significantly less expensive than PBT, but PET’s processing sensitivity — particularly its strict drying requirement — increases operational cost in production environments where drying process control is marginal. PBT’s slight cost premium over PET often pays back in lower processing reject rates.
Recycling und Nachhaltigkeit
Both PA and polyester are thermoplastics and therefore recyclable by re-melting. PET has the most mature recycling infrastructure globally — post-consumer PET bottles are routinely recycled into fiber, film, and packaging applications. PA recycling infrastructure is less developed, though closed-loop recycling programs exist in the automotive sector.
Bio-based variants of both materials are available: bio-PA (polyamide 11 from castor oil, available as PA11) and bio-PET (partially or fully bio-derived from sugarcane ethylene). These grades carry a cost premium of 20–50% over petroleum-derived equivalents but offer reduced lifecycle carbon footprint for manufacturers with sustainability commitments.
Injection Molding PA and Polyester at Fecision
Fecision molds both polyamide and polyester grades — from standard PA6 and PBT for industrial applications through to PA66-GF30 for automotive structural components and PETG for medical packaging. The same ISO 9001:2015-certified quality system governs material traceability, process validation, and dimensional inspection for both material families.
- Polyamide grades in production: PA6, PA66, PA12, PA66-GF30 — automotive under-hood components, gear housings, cable management parts, medical tubing connectors.
- Polyester grades in production: PBT, PBT-GF30, PET, PETG — connector housings, electronic enclosures, automotive sensor bodies, transparent medical packaging trays.
- Materialverwaltung: Dedicated desiccant drying for PA and PET. Gravimetric dosing for glass-fibre and additive consistency. Lot traceability from raw material CoA to finished part.
- DFM-Rezension: Glass-filled grade shrinkage and warpage simulation with Moldex3D before tooling commitment. Processing window definition for both unfilled and reinforced grades.
To make an informed choice between polyamide and polyester, evaluate your needs. Consider strength, durability, and environmental impact. Contact us for material selection advice and DFM review at fecision.com/contact-us.
Häufige Fragen zum Großhandel mit Lebensmitteln und Getränken
Is polyamide or polyester stronger for injection-molded engineering parts?
In dry-as-molded condition, PA66 is stronger than PBT. However, at moisture equilibrium in a humid environment, PA66 tensile strength drops while PBT is unaffected by moisture. For applications in controlled dry environments, PA66 wins. For humid or outdoor environments, the advantage narrows substantially.
Why is PBT preferred over PA for connector housings?
PBT absorbs only 0.07% moisture versus PA66’s 2.5% — meaning PBT connector housings maintain their pin-to-pin spacing across all humidity conditions. PA housings can shift dimensionally by 0.3–0.5 mm from dry to moisture-equilibrated state, potentially exceeding the mating tolerance of fine-pitch connector interfaces.
Can glass-fiber reinforcement be used with both PA and PBT?
Yes — both PA-GF and PBT-GF grades are widely available and commonly used. PA66-GF30 increases tensile strength to 180–200 MPa and HDT to 240–250°C. PBT-GF30 increases HDT to 200–210°C and reduces shrinkage to 0.3–0.8%.
Is PETG suitable for medical applications?
Yes — PETG is widely used for medical packaging trays, diagnostic device housings, and point-of-care instrument components. FDA-compliant grades are available, and PETG resists common hospital disinfectants including isopropanol and dilute bleach.
Referenzen und maßgebliche Quellen
Zugriff im Mai 2026.
[1] BASF SE. Ultramid® (PA) — Product Range and Processing Guide. https://plastics-rubber.basf.com/emea/en/performance_polymers/products/ultramid
[2] DuPont. Zytel® and Minlon® Nylon Resins Molding Guide; Rynite® PET and Rynite® PBT Thermoplastic Polyester Resins Processing Guide. https://docslib.org/download/1772240/dupont-zytel%C2%AE-and-minlon%C2%AE-nylon-resins-molding-guide-table-of-contents
[3] ISO 16396-1:2015. Plastics — Polyamide (PA) moulding and extrusion materials — Part 1: Designation system, marking of products and basis for specifications. https://www.iso.org/standard/56744.html
