Guides / Sourcing
Specifying Machined PEEK for Aircraft Parts
September 26, 2026
Sources: manufacturer datasheets and published standards. See editorial standards.
Aircraft carry more machined plastic than most engineers expect once they start looking at the systems side rather than the airframe. PEEK is the material that shows up again and again in that search, not because it is exotic but because it solves three problems that metal creates on an airplane: weight, heat transfer where you do not want it, and a metal-to-metal path for current where you do not want one either.
What gets machined from PEEK
The parts are almost never structural in the load-bearing sense. They are the hardware around the structure:
- Brackets, standoffs and equipment mounts
- Bushings and spacers, often at a fastener or a pivot
- Cable clamps and hose clamps
- Electrical insulators and connector backshells
- Duct segments and duct supports in air distribution runs
- Static seal rings and glands, as the rigid seal body rather than the elastomer itself
None of this is airframe. It is the hardware that holds wiring, ducting and small equipment in place inside a structure that someone else has already qualified for load.
Why PEEK instead of metal
Weight. PEEK sits at about 1.30 g/cm³ against roughly 2.70 for aluminium and closer to 8 for steel or titanium alloys. On a part with modest load, that difference is not marginal, and it is one of the few weight savings that does not require a redesign of the surrounding structure. The full property set, including where PEEK’s lower stiffness has to be designed around, is in PEEK material properties.
Thermal isolation. Thermal conductivity around 0.25 W/m·K is a small fraction of any metal’s. A PEEK standoff between a hot line and a cold structure, or a PEEK bushing isolating a heat-generating component from a sensitive one nearby, does a job a metal part cannot do without adding an insulating layer on top of it.
No galvanic path. Aircraft mix aluminium, steel, titanium and carbon fibre composite, and every dissimilar metal joint is a corrosion risk in the presence of moisture. A PEEK bushing, washer or standoff at that joint removes the electrical path entirely. It is a small detail that shows up on drawings more often than the part’s size would suggest.
Chemical exposure. Fuel, hydraulic fluid and de-icing fluid all sit near systems hardware at some point, and PEEK tolerates all three at the temperatures involved without the conditioning or coating that some plastics need.
Which grade dominates
Two grades cover most of this work. Unfilled PEEK goes on parts that need to insulate electrically or that see modest load and benefit from toughness, such as connector backshells and lightly loaded clamps. CF30 carbon filled PEEK goes on brackets and mounts that need stiffness and dimensional stability through a thermal cycle, because it expands roughly half as much as unfilled resin per degree and holds a tighter dimension against vibration. The trade is that CF30 is electrically conductive, which rules it out wherever the part is also doing insulation duty. Where stiffness is needed without conductivity, glass filled (GF30) is the usual substitute. The full case for each grade, including the numbers behind that trade, is in which PEEK grade to specify.
Where PEEK is not the answer
Primary structure. Wing ribs, spars, fittings that carry flight loads and anything in the load path between the airframe and its major masses stay metal or composite. PEEK’s modulus is roughly one fiftieth of steel’s, and no filler closes that gap enough to change the answer.
Bearing loads at a fastener without a metal insert. A bolt torqued directly into an unreinforced PEEK boss can crush or creep under sustained clamp load. Where a fastener carries real load, the usual fix is a metal insert or bushing, with PEEK carrying the part around it rather than the joint itself.
Sustained high heat near an engine. PEEK’s continuous service ceiling sits around 250°C. Zones that run hotter than that on a sustained basis call for PI, PAI or a metal part instead.
Anywhere a lightning strike current path is expected. A part that is meant to carry strike current or bond structure electrically needs to stay conductive metal. Replacing it with plastic, filled or not, removes that path.
Getting the spec right the first time
The pattern across all of this is the same one that runs through most aerospace PEEK work: PEEK earns its place in the gaps metal leaves open, on parts that do not carry primary load, and it goes wrong when someone tries to stretch it into a structural role it was never meant to hold.
Send the drawing with the grade, the service temperature and the load case, and we match you with shops that machine aerospace PEEK regularly rather than occasionally.
Frequently asked questions
Can PEEK replace a metal part carrying primary structural load?
No. PEEK belongs in secondary structure, systems and interiors. Primary load paths, the members that carry flight and ground loads through the airframe, stay metal or composite because that is what the structural substantiation is built around.
Which PEEK grade is used most often on aircraft parts?
Carbon filled (CF30) for brackets and mounts that need stiffness and low thermal expansion, unfilled where electrical insulation matters. Glass filled shows up where stiffness is wanted without the conductivity that carbon fibre brings.
Does a machined PEEK part need its own certification to fly?
The resin does not carry an aviation certificate on its own. What matters is that the part traces to a qualified material and process under the aircraft program's own approval, which is a documentation question more than a material one.
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