Engineering Materials Guide
What Is the Density of PEEK? Weight, Strength, and Key Applications
Learn how PEEK density affects part weight, strength-to-weight performance, material selection, and design decisions for aerospace, medical, industrial, and chemical-processing components.
For a custom machined component, density is more than a number on a material datasheet. It affects shipping weight, assembly loads, handling, inertia, and the practical value of replacing metal with a high-performance polymer.
Understanding PEEK: The High-Performance Polymer
Polyether ether ketone, commonly called PEEK, is a semi-crystalline thermoplastic engineered for demanding service conditions. Its molecular structure gives it an unusual combination of thermal stability, chemical resistance, dimensional reliability, and mechanical toughness.
Engineers often ask about PEEK density when they are evaluating a metal replacement or calculating the total weight of a custom component. A lower-density material can reduce moving mass, simplify manual handling, lower the load on an actuator, and improve the efficiency of an assembly. However, density should always be assessed alongside temperature, stress, wear, chemical exposure, and manufacturing requirements.
Design perspective
PEEK is not simply a “light plastic.” Its value comes from retaining useful mechanical performance in environments where many ordinary plastics soften, creep, absorb chemicals, or wear too quickly.
What Is the Density of PEEK?
The standard density of unfilled PEEK is approximately 1.30–1.32 g/cm³. The exact value depends on the resin grade, crystallinity, processing history, and test method, so we recommend using the supplier’s datasheet when weight calculations must be precise.
| Material | Typical density | Engineering implication |
|---|---|---|
| Unfilled PEEK | Approximately 1.30–1.32 g/cm³ | Lightweight, strong, and chemically resistant base grade |
| Aluminum | Approximately 2.7 g/cm³ | PEEK is substantially lighter for an equivalent volume |
| Steel | Approximately 7.8 g/cm³ | PEEK can significantly reduce component mass |
| 30% glass-filled PEEK | Typically higher than base PEEK | More stiffness and lower thermal expansion, with added mass |
| 30% carbon-filled PEEK | Typically higher than base PEEK | Higher stiffness and improved dimensional behavior |
A useful calculation is straightforward: multiply the part volume in cubic centimeters by the material density in grams per cubic centimeter. For example, a 100 cm³ unfilled PEEK component weighs roughly 130–132 g before accounting for tolerances, inserts, or surface features. Filled grades require their own datasheet value because fiber content changes both mass and performance.
PEEK Material Properties: Strength and Durability
PEEK is valued because it combines relatively low density with mechanical properties that are unusually strong for a thermoplastic. Its strength and modulus remain useful across a broad temperature range, although the final result depends on grade, part geometry, crystallinity, moisture exposure, and loading direction.
How strong is PEEK?
Typical unfilled PEEK tensile strength is often in the range of 90–100 MPa, while tensile modulus is commonly around 3.5–4.0 GPa. These are representative values rather than universal design limits. A reinforced grade can provide higher stiffness and strength, but its behavior may become more anisotropic and its machining response may change.
The strength-to-weight ratio is the key comparison. A PEEK part may not match steel in absolute strength, but its much lower density can deliver an attractive ratio of useful mechanical capacity to component mass. This is why designers consider PEEK for brackets, bushings, guides, insulators, and other parts where reducing weight is important without accepting the limitations of commodity plastics.
Impact and fatigue behavior
PEEK offers good toughness and impact resistance, while its fatigue performance can support repeated mechanical cycling when the design controls stress concentration, temperature, and surface condition.
Creep resistance
Compared with many standard thermoplastics, PEEK resists deformation under sustained load more effectively. Filled grades can further improve stiffness and dimensional stability for long-term service.
How Fillers Affect PEEK Density and Performance
PEEK is available as an unfilled resin and in reinforced grades. The most common engineering distinctions are glass-filled PEEK, carbon-filled PEEK, and specialized wear or electrically modified formulations. Fiber reinforcement increases the density compared with the base resin, but it is selected because it changes the mechanical behavior in useful ways.
Unfilled PEEK
The base grade provides the lowest density within this comparison and is often selected for a balanced combination of strength, toughness, chemical resistance, and machinability.
30% glass-filled PEEK
Adding approximately 30% glass fiber shifts density upward from the base-resin level and generally improves rigidity, compressive performance, and resistance to thermal expansion.
30% carbon-filled PEEK
A 30% carbon-fiber grade also has a higher density than unfilled PEEK, while typically delivering greater stiffness, improved dimensional stability, and a lower coefficient of thermal expansion.
Important selection note
Fiber reinforcement is not automatically better. It can increase tool wear, affect surface finish, introduce directional properties, and add weight. We select the grade according to the actual load case, temperature, wear mechanism, and dimensional requirement.
Key Applications of PEEK
The right PEEK application is usually one where ordinary plastics lack temperature, chemical, wear, or long-term mechanical performance. We machine PEEK and other engineering polymers for prototypes, low-volume production, and repeat manufacturing across several demanding industries.
Aerospace
PEEK can reduce mass in cabin interiors, brackets, guides, insulation components, and selected structural or semi-structural applications. Weight reduction is particularly valuable where many small components contribute to total aircraft mass.
Biomedical
Medical-grade PEEK is used in selected implant and device applications because of its biocompatibility, chemical stability, and modulus that can be closer to human bone than many metals. Medical use requires the correct qualified grade and controlled manufacturing route.
Automotive and industrial equipment
Bearings, seals, gears, bushings, rollers, wear strips, and guides may use PEEK where low friction, high heat resistance, dimensional stability, and wear performance are required.
Chemical processing and oil & gas
PEEK resists many harsh fluids and can perform in high-pressure environments, making it useful for fluid-handling components, seals, valve parts, pump components, and insulating elements when the specific chemical compatibility has been verified.
PEEK vs. Other High-Performance Polymers
PEEK is often compared with PEI, commonly known by the trade name Ultem, and PPS. These polymers can all solve demanding engineering problems, but their density, temperature capability, chemical resistance, mechanical retention, and cost are not identical.
| Material | General comparison | When engineers may consider it |
|---|---|---|
| PEEK | Premium performance, strong chemical resistance, high heat capability, and excellent mechanical retention | Severe thermal, chemical, wear, or strength-to-weight requirements |
| PEI | High-performance thermoplastic with strong thermal and dimensional behavior | Electrical, aerospace, and equipment parts where the property balance and cost fit the design |
| PPS | High chemical resistance and strong heat performance, often with a different cost and stiffness balance | Chemical, electrical, automotive, and industrial applications requiring stable performance |
PEEK is frequently called the “gold standard” among engineering polymers because it combines several high-value properties in one material. That performance comes with premium material and machining costs, so we do not recommend it automatically. If PEI, PPS, PAI, or another polymer satisfies the real design requirements, it may provide a more efficient solution.
Frequently Asked Questions (FAQ)
What is the tensile strength of PEEK material?
Typical unfilled PEEK has a tensile strength of approximately 90–100 MPa. Actual results vary by grade, processing, crystallinity, test direction, temperature, and specimen geometry. Reinforced grades can reach higher values, but the datasheet for the selected grade should control design calculations.
What are the applications of PEEK filament?
PEEK filament is used in high-performance 3D printing and rapid prototyping for parts that need heat resistance, chemical resistance, strength, or low wear. Printing PEEK requires careful control of the printer, build environment, thermal conditions, and post-processing, so printed prototypes should be evaluated separately from precision CNC-machined parts.
Is PEEK heavier than aluminum?
No. Unfilled PEEK is significantly lighter by volume: approximately 1.30–1.32 g/cm³ compared with roughly 2.7 g/cm³ for aluminum. The comparison changes when PEEK is filled with glass or carbon fiber, but reinforced PEEK is still generally much lighter than aluminum for the same volume.
Why is PEEK used in medical implants?
Selected medical-grade PEEK is used because of its biocompatibility, chemical stability, suitable mechanical behavior, and radiolucency. Radiolucency allows imaging technologies such as X-ray or CT to view surrounding tissue more clearly than they can through some radiopaque metals. Medical designs must use the appropriate qualified material and manufacturing controls.
Conclusion: Why Density Matters for Engineering Success
The density of unfilled PEEK is approximately 1.30–1.32 g/cm³, making it substantially lighter than aluminum and steel. That lightweight profile becomes especially valuable when combined with PEEK’s high tensile strength, stiffness, chemical resistance, thermal stability, creep resistance, and wear performance.
Filled PEEK grades increase density, but they can also provide the stiffness, lower thermal expansion, and dimensional stability required for a particular component. The best selection balances weight, load, temperature, friction, chemical exposure, tolerance, and total manufacturing cost rather than focusing on one property in isolation.
Before releasing a design
Check the datasheet for the exact PEEK grade, filler percentage, density, tensile properties, thermal limits, and dimensional guidance. Material data can vary meaningfully between manufacturers and formulations.
At PlasticCNCPro, we help global B2B customers evaluate PEEK and other engineering polymers for custom CNC-machined components. Our team reviews drawings, 3D models, tolerances, material requirements, quantity, and application conditions before production. We support prototypes, low-volume parts, and repeat manufacturing for industrial equipment, automation, medical and laboratory devices, automotive systems, fluid-handling equipment, and other precision applications.
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