Complete Filament Properties Guide: Mechanical and Thermal Summary

Why Comparing Filament Properties Is Not Simple

Every filament property table you find online shows a single number per material—but those numbers come from test specimens printed under ideal conditions. Real-world performance depends on layer orientation, print temperature, cooling, and infill. That said, TDS data is still the best starting point for narrowing choices, and the differences between polymer families are large enough to matter even with real-world variation.

This guide covers the two property dimensions that matter most for part selection: mechanical properties (tensile strength, flexural modulus, elongation at break) and thermal properties (heat deflection temperature, glass transition temperature). Print settings are covered separately where relevant.

Mechanical Properties by Polymer Family

Tensile Strength

Tensile strength (MPa) tells you how much pulling force a material can withstand before breaking. Higher is generally better for structural parts, but brittleness (low elongation at break) can matter more than raw strength for parts that see impact.

The PA spread (36–173 MPa) reflects a huge range of formulations: unreinforced PA12 sits around 50–60 MPa, while carbon-fiber-filled PA6 grades like eSUN PAHT-CF reach 173 MPa. Similarly, PEEK variants span 72–145 MPa—FormFutura LUVOCOM PEEK CF 9676 tops out at 145 MPa versus 72 MPa for unfilled base-grade PEEK.

The PLA spread (10–75 MPa) reflects quality variation and specialty formulations. Carbon-fiber PLA like R3D PLA-CF reaches 75 MPa, while low-quality or wood-filled PLAs can drop to 24 MPa. Most standard PLA sits in the 40–55 MPa range.

Flexural Modulus (Stiffness)

Flexural modulus (MPa) measures resistance to bending. High modulus = stiff parts that don't deflect under load. Low modulus = flexible parts that can absorb deflection. This property is often more decisive than tensile strength for functional parts that must hold shape.

Carbon-fiber reinforced grades dramatically increase flexural modulus. 3DXTech CarbonX PP+CF reaches 6,100 MPa (vs ~1,500 MPa for unfilled PP). 3DXTech FibreX PEEK+GF20 hits 7,625 MPa. TPU stands out as an intentional outlier—its 23–800 MPa modulus range is the point: it's designed to flex, not hold shape.

Elongation at Break (Ductility vs. Brittleness)

Elongation at break tells you how much a material stretches before snapping. Low elongation = brittle (PLA, carbon-fiber grades). High elongation = tough, impact-resistant. For parts that must survive drops or impacts, elongation is often more important than tensile strength.

PETG's average elongation of 40% is why it's so popular for functional parts: it won't shatter on impact the way PLA does (avg 14%). 3DJAKE easyPETG measures 31% elongation with 53 MPa tensile strength—a combination ABS rarely matches with similar ease of printing.

Thermal Properties by Polymer Family

Heat Deflection Temperature (HDT)

HDT (°C) is the temperature at which a loaded test specimen deflects by 0.25mm under a specified load (typically 0.45 MPa or 1.8 MPa—always check which standard a manufacturer uses). It's the most practical single number for asking "how hot can this part get before it sags?"

The PA range (50–240°C) is wide because glass-fiber and carbon-fiber filled grades fundamentally transform the thermal profile. FormFutura LUVOCOM PAHT CF 9742 reaches 200°C HDT; unreinforced PA6 can sit as low as 50°C when moisture-conditioned. If you need PA for heat resistance, specify a CF or GF grade.

PLA's range (45–137°C) includes annealed and HT-post-processed variants. Standard off-the-shelf PLA sits at 52–60°C—well below a car interior in summer (~80–90°C). Extrudr GreenTEC Pro (an HT-PLA) reaches 115°C HDT after annealing.

Glass Transition Temperature (Tg)

Tg is where an amorphous polymer transitions from glassy to rubbery. For semi-crystalline polymers (PA, PP, PEEK), Tg is less meaningful than HDT. Fewer materials in our database report Tg vs HDT, but key reference points from available data:

Data Deep Dive: How the Numbers Shift with Reinforcement

Carbon fiber (CF) and glass fiber (GF) reinforcement consistently boost stiffness and heat resistance while reducing elongation. Here's what the data shows across our database for key polymers where we have both base and reinforced grades:

PETG: Base vs CF Grade

Standard PETG averages 48.7 MPa tensile, 2,052 MPa flexural modulus, 72°C HDT (from 90 materials). PETG-CF grades in our database (e.g. Fiberlogy PETG+CF at 105 MPa tensile, 69°C HDT; Polymaker PolyCore PETG-1113 at 100 MPa, 78°C HDT) show tensile strength roughly doubling. However, elongation at break drops from ~40% to ~3%—a significant brittleness trade-off.

PA: Unreinforced vs CF/GF Grade

Unreinforced nylons (PA6, PA12) typically sit at 50–65 MPa tensile, 50–100°C HDT depending on moisture content. CF-filled PA grades like 3DXTech CarbonX PA6+CF Gen3 (63 MPa, 147°C HDT, 3,750 MPa flexural modulus) and 3DXTech CarbonX PA12+CF (72 MPa, 150°C HDT, 7,900 MPa flexural modulus) are in a different performance class entirely. For load-bearing applications above 100°C, a CF-PA grade is almost always required.

ASA: Underrated for UV + Heat

ASA's HDT of 76–105°C (avg 91°C across 44 materials) combined with its UV resistance makes it unique. 3DJAKE ASA CF reaches 93°C HDT with 62 MPa tensile—useful for outdoor enclosures that also see mechanical load. 3DXTech 3DXMAX ASA at 95°C HDT and 45 MPa is a more typical unfilled baseline.

Polymer Fingerprint: Visual Overview

Bottom Line: Choosing by Property Priority

Use this decision framework based on which property is your binding constraint:

One important caveat: the PA dataset (98 materials in our database) and PETG dataset (121 materials) are large enough to draw robust conclusions. PEEK (14 materials), PEI (16 materials), and HIPS (9 materials) are smaller samples—treat their averages as directional rather than definitive.