Top PEEK Thermal Properties Buyers Should Know?
PEEK thermal properties deserve careful attention because they influence part life, processing stability, and total operating cost. Buyers often focus on a datasheet’s maximum continuous-use temperature. That number matters, but it rarely tells the whole engineering story. A PEEK component inside a pump, valve, bearing, or electrical connector may face heat, pressure, friction, chemicals, and repeated temperature changes at once.
Dr. Tim A. Osswald, a respected polymer processing expert, explains the practical principle clearly: “Processing history matters because it changes polymer structure.” This point is easy to overlook. Mold temperature, cooling speed, annealing, reinforcement, and moisture control can alter crystallinity and dimensional behavior. Two parts made from the same PEEK grade may not perform identically. That deserves attention.
This guide examines the PEEK thermal properties buyers should compare before approving a material. It covers glass-transition temperature, melting temperature, continuous service temperature, thermal conductivity, expansion, and heat deflection behavior. It also considers filled grades, including glass-fiber and carbon-fiber reinforced PEEK. These materials can improve stiffness and heat transfer, yet they may increase anisotropy or wear against mating surfaces.
A datasheet is only a starting point. Real performance depends on geometry and processing. Buyers should request test conditions, not isolated figures. They should also review thermal cycling results when the part repeatedly moves between cold storage and high operating temperatures. Small assumptions can become expensive failures. That is not dramatic; it is common engineering reality.
What Is PEEK and Why Do Its Thermal Properties Matter?
PEEK, or polyether ether ketone, is a high-performance engineering thermoplastic. Its molecular structure gives it strong heat resistance, chemical stability, and mechanical strength. PEEK is also semicrystalline, so its final properties depend on cooling speed, processing temperature, and part geometry.
Its glass-transition temperature is about 143°C, while its melting point is near 343°C. These figures matter when a component faces repeated heating, friction, or pressure. For example, a PEEK bearing cage near a hot motor may resist softening better than ordinary plastics. It can maintain shape under heat, but it is not immune to creep. Long exposure can still reduce stiffness. That detail is often underestimated.
Tips: Check both continuous and peak temperatures. Do not select PEEK from melting data alone. Review load, heating cycles, wall thickness, and cooling conditions. A thick molded section may cool unevenly and develop internal stress. Testing a real sample is wiser than trusting a datasheet blindly. Small processing errors can become large dimensional changes later.
In practical design work, thermal expansion also deserves attention. PEEK expands more than metals, although reinforcement can reduce this movement. A tight metal-to-PEEK fit may work at room temperature but bind after heating. I have seen temperature assumptions cause more trouble than the material itself. Thermal properties should be measured against the complete operating environment, not viewed as isolated numbers.
What Is PEEK and Why Do Its Thermal Properties Matter?
PEEK, or polyether ether ketone, is a high-performance engineering thermoplastic known for excellent heat resistance, dimensional stability, chemical resistance, and mechanical strength. Its glass transition temperature indicates when the material begins to soften, while its continuous-use temperature helps define long-term operating capability. The melting temperature is important for processing and molding.
Typical reference values for unfilled PEEK: actual values may vary with grade, processing method, test standard, and application conditions.
How PEEK Performs Across Different Temperature Ranges
PEEK performs differently as temperature rises, so buyers should read beyond its headline heat rating. Industry datasets using ASTM D3418 place its glass-transition temperature near 143°C and melting point near 343°C.
Below 100°C, PEEK usually retains strong stiffness, low moisture sensitivity, and stable dimensional behavior. This range suits precision components with repeated movement.
Between 100°C and 200°C, strength gradually declines, especially under continuous mechanical load. Published UL 746B thermal-aging evaluations commonly place long-term service capability near 250°C, depending on grade, stress, and environment.
At 250–300°C, short-term exposure may remain practical, but creep becomes a serious design concern. Above its melting point, the polymer flows completely. That sounds obvious, yet designers sometimes confuse melting temperature with safe operating temperature.
Tips:
Check load, exposure time, and chemical contact together. Request ASTM D638 tensile data at the actual service temperature. Compare unfilled and reinforced grades carefully. A fiber-filled option may improve stiffness, but it can increase anisotropy and wear against mating parts. Thermal cycling also deserves testing; one static heat result cannot predict every field condition. In my experience, a component surviving 280°C for ten minutes proves little about surviving 220°C for five years. That distinction is easy to miss. Use finite-element analysis for stress prediction, then validate the result with accelerated aging and dimensional measurements. Data sheets are useful starting points, not final design evidence.
Key Thermal Properties of PEEK Buyers Should Compare
When comparing PEEK grades, buyers should start with glass-transition temperature, melting point, and heat-deflection temperature. Standard unfilled PEEK typically shows a glass-transition temperature near 143°C and a melting point around 343°C. These figures are reported in polymer data records using ISO 11357 and ASTM D3418 methods. Heat-deflection temperature may exceed 140°C under specified loading, but test pressure changes the result significantly.
Look beyond headline numbers. Published CAMPUS database data commonly lists thermal conductivity near 0.25 W/m·K for unfilled PEEK. This low conductivity can help limit heat transfer, yet it may slow heat removal around bearings or enclosed electrical parts. The linear thermal expansion coefficient is often about 45–50 × 10⁻⁶/K. Reinforcing fibres can reduce expansion, but they may create directional movement and uneven stress.
Service temperature needs careful interpretation. Long-term exposure near 250°C is frequently cited in engineering data, while short-term peaks may reach higher levels. That difference matters. A thermal report from a supplier is not automatically comparable to an ISO or ASTM result. Ask for conditioning time, specimen direction, load, and heating rate. Small omissions can distort purchasing decisions. In actual testing, moisture and machining history can also influence dimensional stability. The uncomfortable part is that one “best” grade rarely exists. Bears.
Top PEEK Thermal Properties Buyers Should Know? - Key Thermal Properties of PEEK Buyers Should Compare
Typical thermal-property values for unfilled, injection-molding-grade PEEK. Actual performance varies with grade, crystallinity, processing history, specimen geometry, temperature, and test method.
| Thermal Property |
Typical Value or Range |
Common Unit |
Typical Test or Reference Method |
Why Buyers Should Compare It |
| Glass Transition Temperature (Tg) |
Approximately 143°C |
°C |
DSC or DMA; ISO 11357 / ISO 6721 |
Indicates the temperature at which the amorphous phase begins to soften and mechanical stiffness can decline. |
| Melting Temperature (Tm) |
Approximately 343°C |
°C |
DSC; ISO 11357 |
Helps define the processing window and distinguishes PEEK from lower-temperature engineering thermoplastics. |
| Continuous Service Temperature |
Approximately 250–260°C |
°C |
Application-dependent; long-term thermal aging evaluation is recommended |
Provides a practical screening value for prolonged exposure, but the allowable temperature also depends on stress, atmosphere, geometry, and service life. |
| Heat Deflection Temperature |
Approximately 150–155°C at 1.8 MPa |
°C |
ISO 75-1 / ISO 75-2 or ASTM D648 |
Shows resistance to deformation under a specified load and is useful for comparing short-term structural performance at elevated temperature. |
| Thermal Conductivity |
Approximately 0.25 W/(m·K) |
W/(m·K) |
ISO 22007-2 or ASTM E1461 |
Low conductivity makes unfilled PEEK a thermal insulator; filled grades can have substantially different heat-transfer behavior. |
| Specific Heat Capacity |
Approximately 1.3 kJ/(kg·K) near room temperature |
kJ/(kg·K) |
DSC; ISO 11357-4 |
Important for estimating heating and cooling energy, cycle time, and temperature rise during operation. |
| Thermal Diffusivity |
Approximately 0.15 mm²/s |
mm²/s |
Calculated from conductivity, density, and specific heat, or measured by laser flash |
Describes how quickly heat spreads through the material and supports thermal-response and molding simulations. |
| Coefficient of Linear Thermal Expansion |
Approximately 45–50 × 10−6 K−1 below Tg |
10−6/K |
ISO 11359 or ASTM E831 |
Supports dimensional-tolerance, seal, bearing-clearance, and thermal-expansion calculations. |
| Thermal Decomposition Behavior |
Generally stable under recommended processing conditions; decomposition increases at excessive temperatures and long residence times |
Qualitative / application-dependent |
TGA; ISO 11358 or ASTM E1131 |
Helps buyers assess processing safety, residence-time limits, discoloration risk, fumes, and long-term thermal aging requirements. |
| Crystallinity Effect |
Crystallinity can increase stiffness, dimensional stability, and resistance to heat-related deformation |
Qualitative / percentage-dependent |
DSC; ISO 11357 |
Two parts made from the same polymer can show different thermal performance because cooling rate and post-molding annealing affect crystallinity. |
Buyer note: Use these figures for preliminary material screening only. For a final selection, request the supplier’s current datasheet and confirm values using the intended grade, part geometry, processing conditions, load level, environmental exposure, and applicable test standard.
How PEEK Thermal Performance Varies by Grade and Reinforcement
PEEK’s thermal performance changes noticeably with grade and reinforcement. Unfilled PEEK typically has a glass-transition temperature near 143°C and a melting point around 343°C. Industry data compiled under ISO 11357 testing also places its thermal conductivity near 0.25 W/m·K. That low conductivity helps limit heat transfer, but it can slow cooling in thick parts.
Reinforcement changes the picture. A 30% glass-fiber grade can reduce molding shrinkage and improve dimensional stability, while its thermal expansion may fall toward 25–35 × 10⁻⁶/K, according to comparative engineering-materials datasets published in 2024. Carbon-fiber grades usually provide lower expansion and faster heat spreading. Reported conductivity can approach 0.8–1.0 W/m·K, depending on fiber loading and orientation. Direction matters. A molded panel may expand differently along and across the flow path.
High-temperature performance is not one number. Long-term service limits often sit near 250°C, but load, oxygen, pressure, and exposure time can change the result. ISO 2578 aging evaluations show why continuous-use claims need careful interpretation. A reinforced grade may resist creep better, yet become more abrasive to tooling and less forgiving during machining. That trade-off is easy to miss. Test data also varies between laboratories, so buyers should request the actual specimen direction, conditioning method, and thermal cycle. In practice, the “best” grade may still fail if the part design traps heat or ignores anisotropic shrinkage.
