PI
also Kapton, Vespel
PI (polyimide) is an aromatic imide-backbone ultra-high-temperature material, typified by Kapton film and direct-formed Vespel SP stock (SP-1 unfilled, SP-21 15 % graphite, SP-22 40 % graphite), with graphite + 10 % PTFE, 15 % MoS2, CF30 and thermoplastic TPI variants.
PI grades and fills
PI is supplied in 6 conditions, soft to hard.
Compare all 6 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
15% Graphite + 10% PTFE (Vespel SP-211) | Pick for the lowest dry coefficient of friction and best start-up/oscillating unlubricated sliding performance. | 44 | 3.5 | 85 Shore D | |
40% Graphite filled | Choose for the best dimensional stability, lowest CTE and highest thermal conductivity in high-load/high-speed bearings and seal rings. | 52 | 3 | 115 HRM | |
15% MoS₂ filled | Use in vacuum, dry gas or inert atmospheres where graphite loses lubricity (moisture-free wear). | 62 | 4 | 87 Shore D | |
15% Graphite filled | Standard bearing/wear grade: lower friction and wear rate than SP-1 with better dimensional stability, no longer an insulator. | 65 | 4.5 | 110 HRM | |
Thermoplastic polyimide, injection-moldable | Use when complex net-shape parts must be injection molded and 240–260 °C service is enough; melt-processable unlike Kapton/Vespel PI. | 92 | 40 | ||
30% carbon-fiber reinforced polyimide | Choose for maximum stiffness, creep resistance and lowest CTE in structural high-temperature parts. | 100 | 2 |
Supply forms, finishes and certifications
Ways PI is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
FILM | PI film | Supply form |
UnfilledDefault | Natural polyimide | Standard supply |
What is PI?
PI (polyimide) is an aromatic imide-backbone ultra-high-temperature material, typified by Kapton film and direct-formed Vespel SP stock (SP-1 unfilled, SP-21 15 % graphite, SP-22 40 % graphite), with graphite + 10 % PTFE, 15 % MoS2, CF30 and thermoplastic TPI variants. It runs continuously at 260 °C and briefly to 480 °C; unfilled values are 1.43 g/cm3, 86 MPa tensile strength, 7.5 % elongation, 3 GPa modulus and 0.29 W/m·K, with high dimensional stability, radiation resistance, low outgassing and good dielectric properties. It does not melt or flow, so parts are machined from isostatically pressed and sintered stock; cost is very high, resistance to strong alkalis and high-temperature steam or hot water is poor, and notched impact is only moderate. PI has a density of 1.43 g/cm³ (0.0517 lb/in³), heavier than 84% of polymer grades. Its glass-transition temperature is 385°C (725 °F). PI has a tensile strength of 86 MPa (12.5 ksi), stronger than 86% of polymer grades. Elongation at break is 7.5% and the elastic modulus is 3 GPa (0.435 Msi).
What is PI used for?
- Wire and cable insulation film
- Aerospace and satellite structural parts
- Unlubricated bushings and thrust washers
- Seal rings and piston rings for high-temperature service
- Semiconductor process components
- Flexible circuit substrates
- Vacuum and high-radiation fixtures
Advantages
- High service temperature — 260°C (500 °F), better than 97% of polymer grades
- Conducts heat well — 0.29 W/m·K (0.168 BTU/hr·ft·°F), better than 80% of polymer grades
- Good UV / weathering resistance — 60/100, better than 80% of polymer grades
Limitations
- High embodied carbon — 13 kg CO₂/kg, worse than 93% of polymer grades
- Difficult to weld — 5/100, worse than 89% of polymer grades
- Heavy — 1.43 g/cm³ (0.0517 lb/in³), worse than 84% of polymer grades
- Limited formability — 15/100, worse than 79% of polymer grades
PI properties
Typical room-temperature values in the Unfilled condition; bars are the position among polymer grades.
Physical5
PI has a density of 1.43 g/cm³ (0.0517 lb/in³), heavier than 84% of polymer grades. Its glass-transition temperature is 385°C (725 °F).
Mechanical15
PI has a tensile strength of 86 MPa (12.5 ksi), stronger than 86% of polymer grades. Elongation at break is 7.5% and the elastic modulus is 3 GPa (0.435 Msi).
Thermal10
PI is rated for continuous service to 260°C (500 °F). It conducts heat at 0.29 W/m·K (0.168 BTU/hr·ft·°F), better than 80% of polymer grades. Thermal expansion is 52 µm/m·K (28.9 µin/in·°F).
Electrical6
PI is an electrical insulator with a dielectric strength of 22 kV/mm (558.8 V/mil) and a resistivity of 1×10¹⁴ Ω·m.
Chemical & Environmental3
Corrosion resistance is excellent (85/100), better than 65% of polymer grades. UV resistance is good.
Sustainability4
Producing a kilogram of PI takes about 290 MJ of energy and emits 13 kg of CO₂ — more than 95% of polymer grades. Typical recycled content is 0%.
Manufacturability4
PI's machinability is good (65/100, better than 66% of polymer grades); weldability not recommended (5/100); formability poor (15/100).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the polymer family
Yield strength against density for every polymer grade FabDigit runs. PI is highlighted; hover a dot for its name, or open the interactive family chart.
Working with PI
Is PI easy to machine?
Machines dry with sharp polished carbide (PCD for graphite/CF grades), light feeds and good chip clearance; brittle at edges so avoid sharp internal corners and stress-relieve/anneal after heavy cuts.
Can PI be welded?
Not weldable — non-melting (except TPI grades); join by high-temperature epoxy/polyimide adhesive, press-fit or mechanical fastening.
Can PI be formed, bent or molded?
Kapton-type film is cast/extruded and can be laminated or thermoformed only slightly; Vespel-type stock is direct-formed (isostatic pressing + sintering) and then machined; only thermoplastic PI can be injection molded (melt 400–420 °C, mold 180–230 °C, dry resin thoroughly).
Manufacturability
The process limits FabDigit's quote engine applies to PI. Design inside these and the part quotes instantly; outside them it routes to an engineer.
CNC machining
| Machinability | Good65 / 100 |
|---|---|
| ISO material group | N.8 |
| Cutting speed (rough / finish) | 400 / 500 m/min |
| Minimum wall | 0.5 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 10× diameter |
| Best surface (machined / polished) | Ra 0.8 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Not Recommend15 / 100 |
|---|---|
| Weldability | Not Recommend5 / 100 |
Injection molding
| Mold shrinkage | — |
|---|---|
| Wall thickness | — – — |
| Recommended draft | — |
| Pre-drying | — |
PI chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| graphite15 % in SP-21, 40 % in SP-22 | 0 – 40 | 0 |
| PTFE10 % in SP-211 | 0 – 10 | 0 |
| MoS215 % in SP-3 (vacuum grade) | 0 – 15 | 0 |
| carbon fiberstructural CF-reinforced grades | 0 – 40 | 0 |
| polyimide resin (PMDA–ODA type aromatic pyromellitic dianhydride + 4,4'-oxydianiline backbone; unfilled default grade | balance |
What surface finishes work on PI?
Amber natural color needs no coating; can be plasma/alkaline-etch activated for metallization and adhesive bonding; polishes to a fine matte finish, no paint/anodize required.
Surface treatments FabDigit runs on polymer parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Injection Molding Coating
Organic Coating
Metallization / Functional
Equivalent designations
Standards and trade names that resolve to PI in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Trade names
- KaptonVespel
- Also called
- Polyimide
How much does PI cost?
PI is a specialty-cost polymer ($$$$$), pricier than about 99% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
PI — frequently asked
What is PI used for?
PI is typically used for wire and cable insulation film, aerospace and satellite structural parts, unlubricated bushings and thrust washers, seal rings and piston rings for high-temperature service, semiconductor process components and flexible circuit substrates. In short: ultimate aerospace performance.
What is the tensile strength of PI?
PI has a typical tensile strength of 86 MPa (12.5 ksi) — stronger than 86% of polymer grades. Strength varies by condition: see the 6 listed tempers.
Is PI easy to machine?
Reasonably — machinability is rated good (65/100, better than 66% of polymer grades). Machines dry with sharp polished carbide (PCD for graphite/CF grades), light feeds and good chip clearance; brittle at edges so avoid sharp internal corners and stress-relieve/anneal after heavy cuts.
Can PI be welded?
Not readily — weldability is rated not recommended (5/100). Not weldable — non-melting (except TPI grades); join by high-temperature epoxy/polyimide adhesive, press-fit or mechanical fastening.
What surface finishes work on PI?
Amber natural color needs no coating; can be plasma/alkaline-etch activated for metallization and adhesive bonding; polishes to a fine matte finish, no paint/anodize required.
Can PI be formed, bent or molded?
Kapton-type film is cast/extruded and can be laminated or thermoformed only slightly; Vespel-type stock is direct-formed (isostatic pressing + sintering) and then machined; only thermoplastic PI can be injection molded (melt 400–420 °C, mold 180–230 °C, dry resin thoroughly).
What is the maximum service temperature of PI?
PI is rated for continuous use to about 260°C (500 °F), and briefly to 480°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does PI cost?
PI is a specialty-cost polymer ($$$$$), pricier than about 99% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in PI?
Yes — PI is available for CNC machining, sheet metal and injection molding with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- Vespel SP-1 / SP-21 / SP-22 / SP-211 / SP-3 polyimide parts and shapes design handbook — DuPont (2021)
- Kapton HN polyimide film — summary of properties — DuPont (2022)
- Duratron PI / CU60 polyimide stock shapes datasheet — Mitsubishi Chemical Advanced Materials (2022)
- Meldin 7001 / 7211 / 7220 polyimide datasheets — Saint-Gobain Performance Plastics (2021)
- AURUM thermoplastic polyimide product guide — Mitsui Chemicals (2020)
- Engineered Materials Handbook Vol. 2: Engineering Plastics — ASM International (1988)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.