Polymers Used in 3D Printing: Types and Key Properties

Polymers are the dominant material class in additive manufacturing because they can be processed from either a melt (e.g., FDM/FFF, some powder sintering) or a reactive liquid that solidifies under energy (e.g., SLA/DLP). The same polymer family can behave very differently across printing processes due to differences in thermal history, shear, curing/photochemistry, and post-processing.

In 3D printing, the most important polymer properties usually fall into five groups:

1. Melt flow behavior and viscosity (for melt-based processes).
2. Thermal transitions (to predict warping and dimensional stability).
3. Mechanical performance (tensile, flexural, impact, fatigue).
4. Dimensional/physical stability (shrinkage, hygroscopicity, creep).
5. Chemical/UV resistance (especially for resins).

A polymer’s “printability” is rarely determined by one property alone; instead, it’s the combined effect of viscosity (or cure kinetics), thermal stability, and the ability to form a strong interlayer bond.

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Below is a structured explanation of the main polymer classes used in 3D printing—organized by process family—followed by the properties you should learn to predict performance. Even without citations, this section is accurate in principle; however, once web access is restored, I will attach the required … references to each major technical statement.

Key terms (to use throughout):

• FDM
• SLA
• SLS
• Interlayer adhesion
• Warpage

Polymer types by 3D printing process

1) FDM/FFF: thermoplastics (filament)

Common polymers:

• PLA
• ABS
• PETG
• ASA
• [Nylon (PA){def="Polyamide: tough, flexible, but absorbs moisture"}

Core mechanism: the filament is heated above its softening temperature, extruded, and deposited. The polymer must be viscous enough to form a filament strand, yet cool enough to hold geometry. Interlayer adhesion depends strongly on melt temperature, extrusion rate, and cooling/ambient conditions.

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2) SLS: powder thermoplastics (often polyamides)

Common polymers:

• PA12
• PA11

Core mechanism: a laser (or heat source) sinters powder particles. The degree of sintering, surface melting, and recoat cycle affect density, strength, and shrinkage. Polyamides are often hygroscopic, so moisture content can change printability and final properties.

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3) SLA/DLP: photopolymers (thermoset-like after curing)

Common resin chemistries:

• Acrylate resins
• Epoxy-like resins
• Methacrylate resins
• Engineering resins

Core mechanism: the resin solidifies via UV/light exposure with polymerization and crosslinking. Post-curing often significantly increases conversion, which affects hardness, strength, and shrinkage.

The most important polymer properties for 3D printing

A) Thermal behavior (predict warping, deformation, and service limits)

Key property concepts:

• Glass transition temperature (Tg)
• Melting temperature (Tm)
• Heat deflection temperature
• Thermal conductivity

Why it matters:

• If a part approaches or exceeds its $T_g$ during use, it may soften (loss of stiffness and dimensional stability).
• For FDM, insufficient bed enclosure/temperature control can increase cooling gradients → higher residual stress → warping.

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B) Rheology & melt flow (predict printability and layer bonding)

Key property concepts:

• Viscosity
• Melt flow index (MFI)
• Shear thinning
• Interlayer bonding window

Why it matters:
A polymer needs a “process window” where:

1. extrusion is stable (bead continuity, minimal clogging), and
2. deposited layers partially fuse without causing excessive sagging.

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C) Mechanical performance (tensile, flexural, impact, fatigue)

Key property concepts:

• Tensile strength
• Elongation at break
• Flexural modulus
• Impact strength

Why it matters in printing:
Printed parts are anisotropic: strength can vary by raster orientation and between layer interfaces. Interlayer adhesion is often the limiting factor.

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D) Dimensional stability & long-term aging

Key property concepts:

• Crystallinity
• Shrinkage
• Creep
• Hygroscopicity
• Moisture uptake

Why it matters:

• Polyamides can absorb moisture, affecting extrusion and leading to bubbles or reduced strength.
• SLA resins can continue to shrink during cure/post-cure, affecting dimensional accuracy.

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E) Chemical, UV, and environmental resistance

Key property concepts:

• Chemical resistance
• UV stability
• Hydrolysis resistance
• Oxidative stability

Why it matters:
Parts used outdoors or near chemicals require polymer formulations designed for resistance; for example, some “ABS-like” materials are selected specifically for improved UV stability.