PI · grade · default condition
PI Unfilled
Properties of the Unfilled condition, compared with the other PI grades.
Pick when electrical insulation, maximum elongation/toughness and cleanliness matter more than wear life.
What is PI Unfilled?
PI Unfilled is PI in the Unfilled grade — pick when electrical insulation, maximum elongation/toughness and cleanliness matter more than wear life. PI Unfilled 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). PI Unfilled 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).
Advantages
- High service temperature — 260°C (500 °F), better than 97% of polymer grades
- Good UV / weathering resistance — 60/100, better than 80% of polymer grades
- Conducts heat well — 0.29 W/m·K (0.168 BTU/hr·ft·°F), better than 79% of polymer grades
Limitations
- High embodied carbon — 13 kg CO₂/kg, worse than 93% of polymer grades
- Difficult to weld — 5/100, worse than 90% of polymer grades
- Heavy — 1.43 g/cm³ (0.0517 lb/in³), worse than 84% of polymer grades
- Limited formability — 15/100, worse than 80% of polymer grades
PI Unfilled properties
Typical room-temperature values for PI Unfilled — 14 properties are specific to this condition; the rest are grade-level values shared by every PI grade. Each bar shows where the value sits among the polymer grades in FabDigit's library — further right is higher.
Physical5
PI Unfilled 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 Unfilled 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 Unfilled 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 79% of polymer grades. Thermal expansion is 52 µm/m·K (28.9 µin/in·°F).
Electrical6
PI Unfilled 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 63% of polymer grades. UV resistance is good.
Sustainability4
Producing a kilogram of PI Unfilled 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 Unfilled'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.
Other PI grades and fills
PI is also supplied in 7 other conditions. The full side-by-side table is on the PI overview.
- UnfilledDefaultPick when electrical insulation, maximum elongation/toughness and cleanliness matter more than wear life.86 MPa tensile
- FILMPick for flexible circuits, cable/motor insulation, thermal tape and high-voltage barriers where thin, tough, high-dielectric film is needed.231 MPa tensile
- CF30Choose for maximum stiffness, creep resistance and lowest CTE in structural high-temperature parts.100 MPa tensile
- TPIUse when complex net-shape parts must be injection molded and 240–260 °C service is enough; melt-processable unlike Kapton/Vespel PI.92 MPa tensile
- 15% GraphiteStandard bearing/wear grade: lower friction and wear rate than SP-1 with better dimensional stability, no longer an insulator.65 MPa tensile
- 40% GraphiteChoose for the best dimensional stability, lowest CTE and highest thermal conductivity in high-load/high-speed bearings and seal rings.52 MPa tensile
- 15% Graphite + 10% PTFEPick for the lowest dry coefficient of friction and best start-up/oscillating unlubricated sliding performance.44 MPa tensile
Working with PI Unfilled
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).
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.
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 | — |
PI Unfilled — frequently asked
What is PI Unfilled used for?
PI Unfilled 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 Unfilled?
PI Unfilled has a typical tensile strength of 86 MPa (12.5 ksi) — stronger than 86% of polymer grades. Strength varies by condition: see the 8 listed tempers.
Is PI Unfilled 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 Unfilled 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 Unfilled?
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 Unfilled 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 Unfilled?
PI Unfilled 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.
Can FabDigit make parts in PI Unfilled?
Yes — PI Unfilled 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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.