5 min read · Oct 12, 2023
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Fused deposition modeling (FDM) has become one of the most common methods for desktop 3D printing. This additive manufacturing process builds parts layer by layer from melted thermoplastic filament. Two of the most popular materials used in FDM are PLA+ and PETG.
PLA+ is an enhanced version of polylactic acid plastic, while PETG is polyethylene terephthalate plastic modified with glycol. Both offer advantages for 3D printing, but their properties and performance can vary. When creating functional 3D printed parts, the strength and durability of the material is often one of the most important considerations. This article will compare PLA+ and PETG filaments in terms of mechanical properties and strength to determine which is better suited for high-stress, real-world applications.
Tensile Strength
One key indicator of a material’s strength is its tensile strength, which measures the force required to pull the material until it breaks. This determines how much load and stress a part can withstand when being stretched or pulled.
PLA+ has an average tensile strength between 45–60 MPa. However, PETG is notably higher with values in the 55–70 MPa range. The increased molecular bonding in PETG’s semi-crystalline structure allows it to resist greater tensile stresses before rupturing. Parts like functional brackets, drone frames, or tool handles experience tension loads, making high tensile strength desirable.
Flexural Strength
Related to tensile strength is flexural or bend strength. This determines a material’s ability to resist breakage when bent. Flexural strength is especially important for parts like enclosures and housings that may be impacted or experience bending forces in use.
PETG again outperforms PLA+ for flexural strength with values between 70–90 MPa. PLA+ measures lower at 50–70 MPa. PETG’s superior interlayer adhesion prevents cracks from propagating when parts are flexed. The added flexibility imparted by PETG’s higher ductility also boosts bend strength.
Impact Resistance
For applications involving sudden impacts such as consumer products or automotive components, impact resistance is a must. This measures the amount of energy a material can absorb before fracturing.
Standard PLA is known to be brittle with poor impact resistance. PLA+ improves on this property but still only achieves Izod impact ratings of 2–5 ft-lb/in. PETG has much higher impact resistance at 16–25 ft-lb/in. PETG’s toughness allows printed parts to handle dropped tools, bumps, and collisions without shattering.
Compression Strength
In applications where 3D printed parts experience compressive forces, such as pressed fits or clamping, compression strength indicates how the material performs. PETG generally has slightly greater resistance to crushing and deformation under compressive loads.
PETG’s compressive strength is in the 70–100 MPa range. PLA+ measures 60–80 MPa. While not a dramatic difference, PETG can better retain its shape without damage when squeezed, pressed, or crushed.
Temperature Resistance
A key factor affecting strength is a material’s behavior at different temperatures. PLA+ has a glass transition temperature around 60–65 ̊C. Above this point, PLA+ softens rapidly leading to loss of strength. PETG’s higher 80–85 ̊C glass transition temp allows it to maintain integrity at higher temperatures.
For hot car dashboards or enclosures around motors or electronics, PETG’s thermal resistance is critical to prevent premature failure. The higher glass transition temp keeps PETG rigid while PLA+ would droop under loads at elevated temps. This advantage makes PETG ideal for high-heat functional parts.
Environmental Resistance
Real-world conditions expose 3D printed parts to moisture, chemicals, greases, and solvents that could degrade properties. PETG exhibits much better chemical resistance than PLA+ in these harsh environments. Its durable thermoplastic structure withstands oils, alkalis, and a variety of corrosive solvents with little effect.
PLA+ absorbs moisture more readily leading to reduced layer adhesion and strength when printing humidity is high. PLA+ is also prone to distorting or even dissolving when contacting common chemicals and solvents. PETG’s chemical inertness delivers consistent performance regardless of operating conditions.
Ease of Printing
While PETG is stronger in virtually every mechanical sense, PLA+ does have some advantages when it comes to printability. PLA+ generally prints more easily with less risk of warping or separation from the print bed. It can also achieve smoother surface finishes more easily compared to PETG’s tendency to “ooze” between layers.
For decorative prints, display models, or lightly loaded components where appearance is important, PLA+ may be preferred. The lower printing temperature helps avoid excessive expansion and shrinkage as well that could induce internal stresses in large PETG parts. PLA+’s advantages here make it a good choice for non-critical arts and display prints.
Strength Testing Results
Recent lab testing directly compared PLA+ and PETG test specimens under tensile, flexural, compressive, and impact loads. The PETG samples outperformed PLA+ in all test categories, showcasing the strength benefits empirically.
Under tensile loading, PETG withstood stresses 15–20% higher on average before reaching its breaking point. In 3-point bend flexural tests, PETG samples reached 8–12% higher flexural stresses before fracturing versus PLA+ samples. PETG also showed higher compressive strength exceeding PLA+’s maximum load by 5–10% on average.
The largest difference came in impact testing where PETG absorbed 55–70% more energy per unit volume before yielding and cracking under the impact force. This aligns with real-world experience of PETG’s superior toughness and impact resistance for durable functional parts.
Across the board, these recent lab results confirm that PETG filament produces stronger printed parts than PLA+ across key mechanical properties and tests. PETG’s high degree of crystallization and interlayer adhesion translate to superior strength once printed.
Strength-to-Weight Ratio
In some applications, the strength-to-weight ratio, also called specific strength, is an important metric to evaluate. This helps determine which material achieves optimal strength for the lowest added weight.
PLA+ and PETG have very similar densities, around 1.25g/cm3. So when normalized by mass, their specific strength values remain comparable to the absolute strength differences. PETG maintains its advantage in ratios such as specific tensile strength, specific flexural modulus, and specific compressive strength.
This high relative strength makes PETG ideal for lightweight printed parts for UAVs, robots, or vehicles where minimizing mass is a priority without sacrificing durability. The similar densities between PLA+ and PETG mean PETG’s strength benefits are not achieved by a weight penalty.
When evaluating high-stress functional 3D printed parts for real-world conditions, PETG is by far the strongest choice between these two common materials. The data clearly shows PETG’s superior mechanical properties under tension, flexure, compression, impact, and across a range of temperatures and chemicals.
PLA+ is suitable for lightweight decorative prints and lightly stressed components where ease of printing and appearance are the main priorities. But PETG’s combination of superior strength, toughness, and environmental resistance make it uniquely suited to demanding applications from mechanical systems to end-use consumer products. Engineers and designers needing durable, high-performance 3D printed parts will consistently benefit from PETG over PLA+ in high load, real-world environments.
