PEEK (polyether ether ketone) is a high-performance plastic that can withstand extreme heat, resist nearly all common chemicals, and match the strength of some metals at a fraction of the weight. It melts at 340°C (644°F) and holds up under continuous use at temperatures that would destroy most other plastics. Originally developed for industrial uses like aircraft components and turbine blades, PEEK has become one of the most important materials in medical implants, electronics, and advanced manufacturing.
What PEEK Is Made Of
PEEK is a semicrystalline thermoplastic polymer, which means it has a partially organized molecular structure and can be melted and reshaped. Its molecular backbone is a chain of aromatic (ring-shaped) carbon structures linked together by two types of chemical bridges: ether groups and ketone groups. This combination gives the name “polyether ether ketone” and is what makes the material so stable and strong.
Because it’s a thermoplastic rather than a thermoset, PEEK can be injection molded, machined from solid stock, or 3D printed. This makes it far more versatile in manufacturing than materials that can only be shaped once. Its density ranges from about 1.31 to 1.54 g/cm³ depending on the grade, making it significantly lighter than steel (around 8 g/cm³) or titanium (about 4.5 g/cm³).
Key Physical Properties
PEEK’s most defining characteristic is its ability to perform in extreme conditions. Its melting point sits at 340°C, and its glass transition temperature (the point where it starts to soften) is around 143°C. Reinforced versions have been tested for continuous use at temperatures up to 250°C, though performance does degrade at the upper end of that range. Tensile strength for standard grades runs between roughly 100 and 130 MPa (about 15,000 to 19,000 psi), which is comparable to some aluminum alloys.
Adding carbon fiber or glass fiber reinforcement pushes those numbers higher. Carbon fiber reinforced PEEK (CFR-PEEK) can match or exceed the strength-to-weight ratio of many metals, which is why it shows up in aerospace and high-performance engineering.
Chemical and Environmental Resistance
PEEK shrugs off an unusually wide range of chemicals. It shows no measurable reaction to common acids like hydrochloric acid (at 10% concentration), phosphoric acid, citric acid, and acetic acid, even at temperatures up to 200°C. The same goes for bases like concentrated sodium hydroxide, alcohols like ethanol and methanol, and solvents like acetone, benzene, and toluene. It also handles steam, gasoline, and salt solutions without degrading.
The short list of chemicals that can damage PEEK includes concentrated sulfuric acid (above 40%), concentrated nitric acid, hydrofluoric acid, bromine, chlorine, fluorine, and phenol. These are aggressive industrial chemicals that most people and most applications will never encounter. For practical purposes, PEEK is resistant to nearly everything it’s likely to contact in service.
This chemical stability also extends to radiation. PEEK resists degradation from gamma radiation and other forms of ionizing radiation, which is one reason it’s used in nuclear and aerospace environments.
Why It’s Popular in Medical Implants
PEEK entered the medical device market in 1998 and has since become a standard material for spinal implants, orthopedic devices, and dental prosthetics. Two properties drive its medical adoption: biocompatibility and radiolucency.
Biocompatibility means the body tolerates it without a harmful immune response. Testing has confirmed that PEEK is not cytotoxic (it doesn’t damage cells). In animal studies, PEEK implanted in muscle tissue for up to twelve weeks produced no adverse tissue response, no infection, and only minimal inflammation, performing comparably to ultra-high-molecular-weight polyethylene, a material already well established in joint replacements. The material also resists degradation from biological fluids, including lipids.
Radiolucency is the other major advantage. PEEK doesn’t show up on X-rays, CT scans, or MRI the way metal does. Metal implants create bright spots and streaks (called artifacts) that can obscure the surrounding bone and tissue, making it difficult for surgeons to evaluate whether an implant has integrated properly or whether complications are developing. PEEK implants produce virtually no artifacts, giving doctors a clear view of the bone-implant interface, bone density changes, and any signs of loosening or bone loss. This clarity allows earlier and more accurate diagnosis of postoperative problems.
PEEK’s stiffness can also be tuned to closely match that of human cortical bone. Metal implants are typically much stiffer than bone, which can cause “stress shielding,” where the surrounding bone weakens because the implant carries too much of the load. PEEK reduces this risk.
Industrial and Aerospace Uses
Before PEEK was a medical material, it was an engineering workhorse. Its combination of heat resistance, chemical stability, and strength-to-weight ratio makes it valuable anywhere conditions are too harsh for ordinary plastics but where metal’s weight or conductivity is a drawback.
In aerospace, PEEK replaces metal in brackets, fasteners, and structural components to save weight. In oil and gas, it serves as seals, valve seats, and pump components that need to survive corrosive fluids at high temperatures. Electronics manufacturers use it for connectors and insulators that must perform reliably in heat. The automotive industry uses it in transmission components, bearings, and under-hood parts exposed to engine heat and aggressive fluids.
3D Printing With PEEK
PEEK can be 3D printed using fused filament fabrication (the same basic process as consumer desktop printers, but with specialized equipment). The challenge is temperature. Standard 3D printers top out around 250°C at the nozzle, but PEEK requires nozzle temperatures of 360 to 400°C to extrude properly. The build chamber also needs to stay heated, typically around 100 to 110°C, to prevent warping and cracking as layers cool.
Research has found that a nozzle temperature of 380°C produces the most uniform and dimensionally accurate prints. Below that, the filament doesn’t fully melt and accumulates internal stress. Above 400°C, the material becomes too liquid and produces distorted, disconnected lines. Printing speed is also much slower than with common plastics, typically around 15 mm/s.
3D printing opens up custom medical implants, patient-specific surgical guides, and complex geometries that would be difficult or impossible to machine from solid stock. It also enables rapid prototyping for aerospace and industrial parts.
Cost and Market Growth
PEEK is expensive compared to standard engineering plastics. Raw material costs are driven by a complex manufacturing process and limited global production capacity. This keeps it in the premium tier, used only where its properties justify the price.
The global PEEK market was valued at $1.41 billion in 2024 and is projected to reach $2.14 billion by 2030, growing at about 7.5% annually. That growth reflects expanding adoption in medical devices, aerospace lightweighting, electric vehicles, and semiconductor manufacturing, all fields where performance at extreme conditions outweighs material cost.