Aerospace Plastics Compared: PEEK, Ultem, PPSU, Delrin, PTFE and More

Last updated: October 7, 2026

Plastics save weight, insulate, slide without lubrication and resist fluids that corrode metal, so aircraft and spacecraft use them for insulators, bushings, seals, spacers and cabin parts. Two filters remove most candidates before any other property is compared: flammability for parts inside an aircraft cabin, and outgassing for parts in a spacecraft. What survives is a short list of seven polymers. AeroCNCParts machines several of them as machined aerospace plastic components, made to the customer’s drawing.

What are aerospace plastics?

Aerospace plastics are engineering and high-performance polymers qualified for the temperatures, loads, fluids and fire or vacuum requirements of flight hardware. They sit at the top of a three-level pyramid:

• Commodity plastics (polyethylene, polypropylene, PVC): cheap, soft, low temperature limits. Rare in machined flight parts.
• Engineering plastics (acetal, nylon, polycarbonate): stable and easy to machine, up to about 100 to 120 °C.
• High-performance plastics (PEEK, PEI, PPSU, PAI, PI and fluoropolymers such as PTFE): service above 150 °C, better chemical resistance, and the grades used for cabin and space parts.

Metals and plastics are ranked together in the top aerospace materials for CNC machining.

Comparison table

Material	Max continuous temp (typical)	Flammability behavior	Outgassing	Wear and friction	Machinability	Typical aerospace parts
PEEK	About 250 °C	Inherently flame resistant	Low in suitable grades	Good	Good; costly stock	Insulators, bushings, wear parts
PEI (Ultem 1000)	About 170 °C	Inherently flame resistant, low smoke	Low in suitable grades	Fair	Good; rigid	Cabin parts, electrical insulators
PPSU (Radel R-5000)	About 180 °C	Flame resistant; used in interior grades	Check by grade	Fair	Good; tough	Interior parts, clips, housings
PAI (Torlon)	About 260 °C	Flame resistant	Low in suitable grades	Very good	Hard; often post-cured	High-load wear parts
PI (Vespel)	About 290 °C	Does not melt; flame resistant	Low	Very good	Costly; brittle in thin sections	Seals, bushings, thermal insulators
PTFE	About 260 °C	Does not support combustion	Low	Lowest friction	Soft; creeps	Seals, liners, insulators
POM (Delrin)	About 100 °C	Burns readily	Check by grade	Very good	Excellent; stable	Spacers, gears, bushings away from flame-critical zones

Values are typical figures from supplier datasheets for unfilled grades. The grade on the drawing and its own datasheet govern.

Material-by-material notes

PEEK

Strong, stiff and resistant to almost every aircraft fluid, with low-outgassing grades for space. Glass- and carbon-filled versions add stiffness and wear resistance. The stock is expensive, so PEEK is chosen where temperature or chemistry requires it; see PEEK parts we machine.

Ultem (PEI)

Inherently flame resistant with low smoke, which makes it the default for many cabin and electrical parts at a lower cost than PEEK. More on Ultem (PEI) parts.

PPSU

Very tough and impact resistant, with good flame behavior; used for some interior parts and clips that must survive repeated handling.

Torlon (PAI)

The highest strength of the unfilled thermoplastics and excellent wear at temperature. It is hard on tools and often needs a post-cure cycle.

Vespel (PI)

A polyimide that does not melt, with service near 290 °C and very low outgassing. It is chosen for seals, bushings and thermal insulators where nothing else survives.

PTFE

The lowest friction of any solid plastic and an excellent dielectric, but soft: it cold-flows under load, so tight tolerances need short, supported features. See PTFE parts.

Delrin (acetal)

Machines cleanly and holds size, at low cost. It is not inherently flame resistant, so it suits parts outside flame-critical cabin surfaces; see Delrin (acetal) parts.

Aircraft interiors: the FAR 25.853 filter

In a transport-category cabin, materials must meet 14 CFR 25.853. Most interior plastics are tested with the vertical burn methods of Appendix F, Part I. Large surfaces such as sidewalls, ceilings and bins must also pass the OSU heat release test (Part IV) and the smoke density test (Part V). Buyers group these as FST: flame, smoke and toxicity.

The test applies to a grade in a given thickness and part configuration, not to a polymer family. No polymer family passes 25.853 as such; a PEI or PEEK grade passes in the configuration tested. A UL 94 V-0 rating is a useful screen but not an aviation approval. Seats add their own constraints, compared in aircraft seat materials.

Space: the outgassing filter

In vacuum, polymers release volatiles that can condense on optics and sensors. ASTM E595 screens materials by total mass loss (TML, 1.0% or less) and collected volatile condensable materials (CVCM, 0.10% or less), and the NASA outgassing database lists results by grade. Cleaning and bake-out follow the customer’s specification. Metals and polymers for orbit are compared in materials for space hardware.

Machining tips for high-performance plastics

• Start from annealed stock, or rough, stress-relieve, then finish, so parts do not warp.
• Set tolerances with thermal expansion in mind: plastics expand several times more than aluminum.
• Use sharp, polished cutters and light finishing passes to limit heat and burrs.
• For space parts, cut dry or with a coolant the customer accepts, to avoid contamination.
• Measure at a stable temperature, after the part has settled.

Quick selection guide

Need	Material
Flame-rated cabin bezel or housing	PEI (Ultem)
Tough interior clip that is handled often	PPSU
High-temperature wear pad	PEEK or Torlon
Extreme temperature seal or bushing in vacuum	Vespel
Low-friction seal or liner	PTFE
Low-cost precise part outside flame-critical zones	Delrin

Need a plastic part machined to print? Send your drawing.

Request a quote for plastic parts

Upload your drawing and 3D model, with the material grade, quantity, any flammability or outgassing requirement and the documentation you need (material certs, FAI, CoC). NDA available on request.

Upload Your Drawing

FAQ

What are aerospace plastics?

High-performance polymers such as PEEK, PEI, PAI, PI, PPSU and PTFE, used where weight, temperature, chemicals, flammability or outgassing requirements rule out commodity plastics.

Is PEEK better than Ultem for aircraft interiors?

Not always. PEI (Ultem) is widely used for flame-rated interior parts at lower cost; PEEK is chosen for higher temperature, strength and chemical resistance.

Is Delrin allowed in aircraft cabins?

Delrin is not inherently flame resistant, so it suits small parts away from cabin surfaces; any cabin use must meet the applicable 25.853 requirements.