PEEK vs PEI (ULTEM) for Aerospace and Industrial Use: Performance Compared

What These Polymers Actually Are

PEEK (polyether ether ketone) is a semi-crystalline thermoplastic that belongs to the PAEK family. Its semicrystalline structure gives it outstanding chemical resistance, near-zero moisture absorption, and mechanical properties that hold up across a wide temperature range. The trade-off: PEEK requires melt temps above 380°C and ideally a high-temperature enclosed printer to achieve good layer adhesion.

PEI — polyetherimide, commercialized by SABIC as ULTEM — is an amorphous thermoplastic. Two grades dominate the 3D printing market: ULTEM 9085 (developed for aerospace, with FAR 25.853 flame, smoke, and toxicity certification) and ULTEM 1010 (the higher-performance variant, with better heat resistance and chemical resistance). Both are harder to print than engineering polymers like nylon, but easier than PEEK because their melt temps are 20–60°C lower.

Both polymers are used in aerospace, defense, and industrial settings where standard engineering materials (ABS, PETG, nylon) simply fail under sustained load or heat.

Thermal Performance: Where the Grades Diverge

Unfilled PEEK in our database shows HDT values of 140–152°C — 3DXTech ThermaX PEEK at 140°C and IEMAI PEEK and iSANMATE PEEK both at 152°C. That is lower than you might expect for PEEK — in bulk injection-moulded form PEEK exceeds 340°C — because FFF printing produces semi-crystalline structures that are never fully crystallised. Proper post-annealing raises the HDT significantly, but as-printed 140–152°C is the realistic baseline.

Carbon fiber and glass fiber filled PEEK grades change the picture dramatically. 3DXTech CarbonX PEEK+CF10 reaches 265°C HDT; 3DXTech FibreX PEEK+GF20 hits 300°C HDT. FormFutura LUVOCOM PEEK CF 9676 reaches 280°C HDT. These are the materials you reach for when the part will see sustained exposure at 200–300°C.

PEI splits cleanly by grade. ULTEM 9085 materials in our database show HDT of 152–175°C — Fiberlogy PEI 9085 at 152°C, FormFutura PEI ULTEM 9085 at 153°C, 3DXTech ThermaX PEI 9085 at 158°C, and iSANMATE PEI 9085 at 175°C. ULTEM 1010 grades perform notably better: 3DXTech ThermaX PEI 1010 and 3DXTech Triton PEI 1010 both at 208°C, Prusament PEI at 207°C, 3DXTech 3DXSTAT ESD-PEI 9085 at 205°C. The glass-filled variant 3DXTech FibreX PEI+GF30 reaches 212°C HDT, and IEMAI PEI 1010 shows 190°C HDT with a vicat softening point of 211°C.

The practical consequence: ULTEM 1010 rivals unfilled PEEK in thermal resistance, but falls well short of filled PEEK grades. If your part must survive above 220°C, filled PEEK is the only FFF option.

Mechanical Strength: Filled Grades Change the Story

Unfilled PEEK tensile strength across our database ranges from 90 to 105 MPa. IEMAI PEEK and iSANMATE PEEK both report 100 MPa; 3DXTech ThermaX PEEK hits 100 MPa with a notably high elongation at break of 28% — an unusually ductile result for PEEK, likely reflecting its as-printed (non-annealed) state. 3DXTech FibreX PEEK+GF20 and 3DXTech CarbonX PEEK+CF10 both reach 105 MPa.

The carbon-filled PEEK variants push significantly higher. FormFutura LUVOCOM PEEK CF 9676 reaches 145 MPa tensile strength. IEMAI CF-PEEK and iSANMATE PEEK CF both hit 112 MPa. Flexural modulus on the filled grades is exceptional: 3DXTech FibreX PEEK+GF20 at 7,625 MPa and 3DXTech CarbonX PEEK+CF10 at 8,300 MPa. These are among the stiffest FFF materials available.

PEI shows a wide range depending on grade and filler. Unfilled PEI 9085 grades are relatively modest: 3DXTech ThermaX PEI 9085 at 54 MPa, IEMAI PEI 9085 at 54 MPa, 3DXTech Triton PEI 9085 at 55 MPa. PEI 1010 unfilled is stronger: 3DXTech ThermaX PEI 1010 at 56 MPa, IEMAI PEI 1010 at 105 MPa. Prusament PEI reaches 95 MPa tensile strength. Fiberlogy PEI 9085 achieves 88 MPa with a remarkable 70% elongation at break — far more ductile than most high-performance materials.

The PEI carbon-fiber reinforced grades are competitive at the top end: 3DXTech CarbonX PEI 1010+CF achieves 145 MPa tensile strength and 7,500 MPa flexural modulus — matching the best PEEK-CF on raw numbers. 3DXTech CarbonX PEI 9085+CF reaches 93 MPa tensile and 8,450 MPa flexural modulus. 3DXTech FibreX PEI+GF30 with glass fiber achieves 8,560 MPa flexural modulus — the highest in our entire PEI dataset.

Printability: Temperature, Hardware, and Process

PEEK demands the most extreme print hardware. Unfilled grades require 380–430°C nozzle temperatures — IEMAI PEEK prints at 390–430°C, iSANMATE PEEK at 390–430°C, and 3DXTech ThermaX PEEK at 380–400°C. Carbon-filled variants: IEMAI CF-PEEK and iSANMATE PEEK CF at 380–420°C. The most extreme is FormFutura LUVOCOM PEEK CF 9676 requiring 450–520°C — a range that rules out all but purpose-built industrial printers. Bed temperatures for PEEK run 130–160°C.

PEI 9085 is more approachable, though still demanding: 3DXTech ThermaX PEI 9085 at 365–385°C, IEMAI PEI 9085 at 360–390°C. Fiberlogy PEI 9085 is the outlier at 350°C. PEI 1010 runs hotter: 3DXTech ThermaX PEI 1010 at 380–400°C, Prusament PEI at 410°C. 3DXTech CarbonX PEI 1010+CF at 385°C.

Both materials require: a hardened steel all-metal hotend (no PTFE past 240°C), an enclosed high-temperature chamber, and thorough filament drying (80–100°C for 6–12 hours minimum). PEI is amorphous, so it doesn't require annealing the way PEEK does to unlock crystallisation. PEEK benefits significantly from a post-print anneal cycle (150–200°C for 1–2 hours) which raises HDT and dimensional stability.

Neither material is suitable for a standard desktop printer. The printer must maintain a chamber temperature of at least 100–120°C to avoid warping and delamination on tall or large parts.

Side-by-Side Comparison

Key property ranges across our database, comparing representative unfilled and filled grades:

Chemical Resistance: PEEK's Major Advantage

Chemical resistance is one area where PEEK's semicrystalline structure provides a clear, practical advantage over amorphous PEI. PEEK is resistant to virtually all industrial fluids including fuels, hydraulic oils, lubricants, steam at elevated pressure, and most acids and solvents. It also absorbs essentially no moisture, which maintains dimensional stability in humid environments.

PEI is resistant to aliphatic solvents and dilute acids, but it is attacked by chlorinated solvents, strong bases, and ketones. ULTEM 9085's specification documentation from SABIC specifically lists susceptibility to certain solvents, which rules it out for parts exposed to common industrial cleaning agents like methylene chloride or acetone.

For aerospace structural parts that will never contact aggressive chemicals — interior cabin components, brackets, tooling fixtures — this distinction rarely matters. For chemical processing equipment, medical sterilization trays (which require steam autoclave resistance), or parts in marine or fuel-adjacent environments, PEEK's chemical resistance is decisive.

Aerospace Certification: The PEI 9085 Case

ULTEM 9085 was specifically formulated to meet FAR 25.853 flame, smoke, and toxicity (FST) requirements for aircraft interiors. This certification is a major reason PEI 9085 dominates aerospace 3D printing despite its lower raw mechanical properties compared to PEI 1010 or PEEK. A part on a commercial aircraft interior isn't just competing on tensile strength — it must pass rigorous burn tests, and demonstrating FST compliance with an FFF-printed part requires either a certified material or a costly testing program.

PEEK also has excellent inherent flame resistance (UL94 V-0 rated in many grades), but PEEK products in the FFF market do not carry the same FST aviation certification history as ULTEM 9085. If your application requires FAA or EASA documentation for an aircraft interior part, PEI 9085 from a qualified supplier is the established path.

For space, defense, and industrial applications that don't require civil aviation certification, PEEK's performance profile becomes more attractive — particularly when chemical resistance or sustained high-temperature operation above 200°C is required.

Cost and Availability

Both materials are expensive compared to engineering polymers, but PEEK is generally 2–4× more costly than PEI 9085 per kilogram at retail. The price difference narrows for specialty filled grades. PEEK filament typically retails at $150–400+ per 500g spool; PEI 9085 filament is typically $80–200 per 500g spool. PEI 1010 sits in between.

Availability has improved: brands like 3DXTech, Fiberlogy, FormFutura, IEMAI, Prusament, and iSANMATE all offer PEI in both grades. PEEK is available from 3DXTech, FormFutura, IEMAI, and iSANMATE in multiple formulations. The choice is no longer limited to Stratasys-compatible formats — both polymers are available in standard 1.75 mm and 2.85 mm diameters for open-filament printers.

When to Use Which

Choose PEEK when:

• Temperature above 200°C is sustained. Unfilled PEEK reaches 140–152°C HDT as-printed, but 3DXTech CarbonX PEEK+CF10 (265°C) and FormFutura LUVOCOM PEEK CF 9676 (280°C) and 3DXTech FibreX PEEK+GF20 (300°C HDT) are the clear leaders for extreme thermal environments. Nothing in the PEI portfolio matches these.
• Chemical resistance is required. Parts exposed to fuels, hydraulic fluids, steam, or strong solvents. PEEK's semicrystalline structure provides dramatically better chemical resistance than amorphous PEI.
• Maximum stiffness in a small cross-section. 3DXTech CarbonX PEEK+CF10 at 8,300 MPa and 3DXTech FibreX PEEK+GF20 at 7,625 MPa flexural modulus represent the upper tier of FFF stiffness. Critical for thin-section parts that must not flex under load.
• Biocompatibility or implant-adjacent applications. Certain PEEK grades are used in medical device manufacturing because the polymer is biocompatible and radiolucent. Verify the specific grade and manufacturer certification before any medical use.

Choose PEI 9085 (ULTEM 9085) when:

• FAR 25.853 FST certification is required. Aircraft interior parts with documented flame, smoke, and toxicity compliance. This is PEI 9085's defining advantage and the primary reason it exists in this form.
• Good balance of heat resistance (150–175°C), strength, and processability. Fiberlogy PEI 9085 at 88 MPa tensile and 152°C HDT is representative; FormFutura PEI ULTEM 9085 at 84 MPa and 153°C HDT. For general aerospace structural testing and tooling that doesn't need extreme heat resistance, 9085 is often sufficient and easier to work with than 1010.
• You need documented material traceability. ULTEM 9085 has a well-established supply chain and material qualification history in aerospace programs. If you're qualifying a material for a production part, 9085 has more flight heritage in additive manufacturing than PEEK does.

Choose PEI 1010 (ULTEM 1010) when:

• Higher heat resistance without moving to PEEK. 3DXTech ThermaX PEI 1010 and Prusament PEI at 207–208°C HDT give meaningful margin over 9085 without the PEEK cost premium or extreme print temperatures.
• Stronger unfilled parts. IEMAI PEI 1010 at 105 MPa and Prusament PEI at 95 MPa are significantly stronger than 9085 unfilled grades (54–62 MPa). If tensile load matters and you don't need FST certification, 1010 is the better unfilled choice.
• Food-contact or autoclave sterilization. ULTEM 1010 is FDA-compliant for food contact and withstands steam autoclave sterilization — valuable for surgical instrument holders, lab equipment, and food processing jigs.

Print Settings Reference

Representative settings across our database:

PEEK (unfilled): Nozzle 380–430°C, bed 130–160°C. Enclosure required (120°C+ chamber preferred). All-metal hardened steel hotend. Anneal at 150–180°C post-print. Dry at 100°C for 6–12 hours before printing. Filament must be kept in a sealed container during printing.

PEEK-CF / PEEK-GF: Nozzle 380–520°C depending on brand. FormFutura LUVOCOM PEEK CF 9676 requires 450–520°C — an industrial printer with a specialty high-temperature nozzle is mandatory. Bed 50–160°C. Diamond or ruby nozzle recommended over hardened steel for very abrasive CF grades.

PEI 9085: Nozzle 350–395°C, bed 130–145°C. High-temp enclosure. All-metal hotend. Dry at 80–100°C for 8+ hours. Fiberlogy PEI 9085 specifies 350°C — the lowest in our dataset and more accessible for printers that top out at 380°C.

PEI 1010: Nozzle 380–410°C, bed 140–160°C. Same enclosure and drying requirements as 9085. Prusament PEI specifies 410°C — at the upper end of what many high-temp desktop printers can sustain.

Our Data Coverage

The Filabase database currently contains 11 PEEK and 15 PEI products. This is a smaller dataset than commodity polymers, reflecting the niche nature of these materials. Tensile data covers 10 PEEK and 13 PEI products; HDT data covers 7 PEEK and 11 PEI products. Flexural modulus data is available for 7 PEEK (including all three 3DXTech PEEK variants) and 10 PEI products. Data coverage for this category is rated medium — we have enough to make reliable comparisons between grades, but individual product-level data can be sparse for some brands.