Rapid Prototyping material comparison: resin versus nylon for functional testing scenarios

Content Menu

● Introduction

● Stereolithography and Resin Basics

● Selective Laser Sintering and Nylon Basics

● Mechanical Property Breakdown

● Real-World Functional Testing Examples

● Decision Framework for Material Selection

● Conclusion

● Frequently Asked Questions

 

Introduction

In product development, the step from CAD to a part you can actually load, drop, or cycle is where most designs either prove themselves or quietly fail. Rapid prototyping has become the standard way to cross that gap quickly, but the choice of material often decides whether the prototype gives useful data or just breaks on the first real test. Two materials dominate functional testing work: photopolymer resins used in stereolithography (SLA/DLP) and polyamide (nylon) powders used in selective laser sintering (SLS). Both are widely available, both produce near-net-shape parts overnight, yet their behavior under load is dramatically different.

This article compares the two from the perspective of engineers who need test results they can trust, not just pretty models. The focus is on tensile behavior, impact resistance, fatigue life, thermal stability, and practical examples from automotive, medical, and consumer-product projects. Data come from peer-reviewed studies and from parts run on common machines such as Formlabs Form 3 series and EOS P-series printers.

Stereolithography and Resin Basics

Stereolithography cures liquid resin layer by layer with a UV laser or projector. Layer thickness typically ranges from 25 µm to 100 µm, and XY resolution can reach 35 µm on high-end machines. After printing, parts require washing in isopropyl alcohol and a final UV post-cure to reach full mechanical properties. Commercial resins now include standard, tough, durable, high-temperature, and flexible formulations. For functional testing, the most used are the “tough” and “durable” types that try to approach ABS-like performance.

Selective Laser Sintering and Nylon Basics

Selective laser sintering fuses nylon powder (usually PA12 or PA11) with a CO₂ laser in a heated chamber. Because unsintered powder supports overhangs, complex geometries can be printed without support structures. Typical layer thickness is 100–120 µm, and surface roughness is higher than SLA, often Ra 8–15 µm after bead blasting. Parts are nearly isotropic because the slow cooling in the powder bed reduces residual stress.

Mechanical Property Breakdown

Tensile Strength and Modulus

Standard tough resins reach ultimate tensile strengths of 55–70 MPa with a modulus around 2.2–2.8 GPa and elongation at break usually below 12 %. Durable-type resins can push elongation to 25–40 % but sacrifice modulus, dropping to 1.0–1.5 GPa. PA12 from SLS typically shows 48–52 MPa tensile strength, modulus 1.7–1.9 GPa, and elongation 15–25 % in the as-printed state. When parts are dried and annealed, elongation often exceeds 40 %.

In a direct head-to-head test on ASTM D638 Type I specimens printed on a Form 3 (tough resin) and an EOS P 396 (PA12), the resin parts failed brittlely at 8–10 % strain while the nylon parts yielded and necked before breaking at 120–180 % strain in the Z direction.

Impact and Toughness

Notched Izod impact values tell the story clearly. Tough resins rarely exceed 25–35 J/m, and many formulations are below 20 J/m. PA12 routinely delivers 60–90 J/m notched and often shows no complete break (hinge break). Unnotched Charpy values for nylon can exceed 100 kJ/m², whereas most resins stay under 30 kJ/m². Drop tests from 1.2 m onto concrete routinely shatter resin prototypes while nylon parts bounce or dent.

Fatigue Performance

Cyclic testing under tension-tension (R=0.1) at 5 Hz reveals another large gap. Resin parts printed in tough formulations typically survive 10⁴–10⁵ cycles at 40 % of ultimate tensile strength before crack propagation. PA12 parts under the same conditions regularly reach 10⁶–10⁷ cycles. The difference comes from the cross-linked network in resins versus the semi-crystalline, chain-entangled structure of nylon.

Thermal Performance

Glass-transition temperature for most functional resins is 60–80 °C; heat-deflection temperature under 0.45 MPa rarely exceeds 70 °C. PA12 maintains useful stiffness above 150 °C and has an HDT of 170–180 °C. In under-hood automotive testing or steam sterilization cycles, this difference eliminates resin from consideration.

Dimensional Accuracy and Surface Finish

Resins win on accuracy and finish. Feature resolution below 0.1 mm and surface roughness Ra < 2 µm are routine. Nylon parts typically hold ±0.2–0.3 mm tolerances and need media blasting or vibro-finishing to reach acceptable smoothness for sliding surfaces.

Real-World Functional Testing Examples

Automotive Air-Intake Duct

A Tier-1 supplier needed to validate flow restriction and vibration durability. Resin prototypes gave perfect internal finish for pressure-drop measurement but cracked at mounting ears after 30 minutes on a shaker table. Switching to PA12 allowed the full 100-hour vibration schedule and revealed a resonance the resin parts never survived to show.

Robotic End-Effector Fingers

Fingers had to grip delicate glass bottles without crushing them. Initial resin versions (flexible-tough blend) achieved the required compliance but fractured after 800 cycles. SLS PA11 with 4 % glass fill survived 50,000 cycles with only minor wear on the contact pads.

Surgical Bone Drill Guide

Accuracy was critical (±0.05 mm on drill trajectories). Resin guides printed in surgical-grade material met the tolerance and allowed intraoperative trial fitting on cadaver bone. The guides were single-use, so brittleness was acceptable.

Wearable Wrist Strap Buckle

The buckle had to survive repeated opening/closing and 1.5 m drops. Resin prototypes passed fit checks but failed drop testing. Nylon buckles passed 10,000 cycles and 50 drops with no visible damage.

Battery Pack Mounting Bracket

Operating temperature reached 85 °C continuous. Resin brackets warped within hours in the environmental chamber. PA12 brackets maintained clamp load and passed 1,000-hour thermal cycling.

Decision Framework for Material Selection

Ask three questions in order:

1. Does the test involve significant impact, flexing, or >50 °C temperatures? → Choose nylon.
2. Is sub-0.1 mm feature resolution or optical clarity required? → Choose resin.
3. Is the part single-use and primarily for fit/form validation? → Resin is usually faster and cheaper.

When answers overlap, hybrid approaches work: print the structural core in nylon and insert or overmold resin details.

Conclusion

Resin and nylon each have clear territories in functional testing. Resin remains the material of choice when extreme detail, tight tolerances, or smooth internal passages are the primary concerns and the loading environment is mild. Nylon dominates whenever the prototype must survive real-world abuse—drops, repeated cycles, elevated temperatures, or chemical exposure. The gap in toughness and fatigue life is simply too large to ignore in demanding applications.

Modern material portfolios have narrowed some differences—new durable resins approach ABS impact levels, and filled nylons can achieve higher stiffness—but the fundamental trade-off persists: cross-linked brittle network versus ductile semi-crystalline polymer. Understanding this trade-off lets engineering teams pick the right tool the first time, reduce wasted prints, and generate test data that actually predicts field performance.

Frequently Asked Questions

Q1: Can I make a resin part tougher by changing print orientation or post-cure time?
A: Orientation helps marginally (XY is strongest), and extended post-cure adds 10–15 % strength, but you still stay in the brittle regime. Toughness does not reach nylon levels.

Q2: Is PA12 safe for skin-contact medical or consumer products?
A: Virgin PA12 passes ISO 10993-5 and -10 for cytotoxicity and irritation with proper cleaning. Many wearable and orthodontic devices already use it.

Q3: How much does moisture affect nylon test results?
A: As-printed PA12 from a good machine is usually 0.2–0.4 % moisture. At 2–3 % absorption, elongation doubles but modulus drops 20 %. Always dry parts before critical testing.

Q4: Are there resins that survive autoclave sterilization?
A: A few high-temperature resins (e.g., Formlabs High Temp or DSM Somos PerFORM) survive one or two 134 °C cycles, but repeated sterilization still favors nylon or PPSF.

Q5: Which material is cheaper for 20–50 identical test parts?
A: Above roughly 15–20 parts, SLS nylon becomes cheaper per part because packing density is high and no supports are needed. Below that volume, resin usually wins.