Vespel SP-21
Vespel SP-21 is the graphite-filled version of DuPont's Vespel polyimide shape stock, with lower friction, better wear resistance and 0.87 W/m·K thermal conductivity — about three times that of unfilled SP-1.
Reference datasheet — Vespel SP-21 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the SP-21 condition
Vespel SP-21 grades and fills
Vespel SP-21 is supplied in 5 conditions, soft to hard. SP-21 is the default FabDigit quotes; the values on this page are for it.
Compare all 5 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
15% graphite + 10% PTFE, lowest friction | Use for dry-running, low-speed start/stop seals and sliding parts needing the lowest static and dynamic friction; the 10 % PTFE cuts tensile strength to 44 MPa and service temperature to 260 °C. | 44 | 3.5 | 85 Shore D | |
40% graphite filled, maximum dimensional stability | Pick for heavily loaded hot bearings and seal rings that need low thermal expansion and 1.5 W/m·K conduction; the 40 % graphite loading drops tensile strength to 52 MPa and machinability to 50. | 52 | 3 | 90 Shore D | |
15% MoS2 filled, vacuum / dry-environment grade | Select for sliding parts in vacuum, dry nitrogen or moisture-free atmospheres where graphite loses lubricity; the 15 % MoS₂ filler holds 288 °C service at 55 MPa tensile strength. | 55 | 4 | 87 Shore D | |
SP-21Default 15% graphite filled | Default pick for high-temperature bearings, seals and washers needing low friction, high PV capability, 0.87 W/m·K heat removal and the dimensional stability given by 15 % graphite. | 65 | 4.5 | ||
Unfilled base polyimide | Choose the unfilled base polyimide for non-rubbing parts needing maximum toughness (86 MPa, 7.5 % elongation) or electrical insulation; thermal conductivity falls to 0.35 W/m·K. | 86 | 7.5 |
What is Vespel SP-21?
Vespel SP-21 is the graphite-filled version of DuPont's Vespel polyimide shape stock, with lower friction, better wear resistance and 0.87 W/m·K thermal conductivity — about three times that of unfilled SP-1. Density is 1.51 g/cm³, tensile strength 65 MPa with 4.5% elongation, and continuous service reaches 288 °C, which covers turbine engine seal rings and bushings. Like all Vespel grades it is direct-formed and sintered from powder, then machined; it cannot be moulded, welded or plated, and moisture pickup must be allowed for in tolerances. SP-1 is the pick when strength and electrical insulation matter more than wear. Vespel SP-21 has a density of 1.51 g/cm³ (0.0546 lb/in³), heavier than 88% of polymer grades. Its glass-transition temperature is 360°C (680 °F). Vespel SP-21 has a tensile strength of 65 MPa (9.43 ksi), stronger than 73% of polymer grades. Elongation at break is 4.5% and the elastic modulus is 3.1 GPa (0.45 Msi).
What is Vespel SP-21 used for?
- turbine engine seal rings
- high-temperature bearings
- bushings in jet engines
Advantages
- High service temperature — 288°C (550 °F), better than 99% of polymer grades
- Conducts heat well — 0.87 W/m·K (0.503 BTU/hr·ft·°F), better than 99% of polymer grades
- Good UV / weathering resistance — 70/100, better than 83% of polymer grades
Limitations
- High embodied carbon — 15 kg CO₂/kg, worse than 96% of polymer grades
- Difficult to weld — 5/100, worse than 89% of polymer grades
- Heavy — 1.51 g/cm³ (0.0546 lb/in³), worse than 88% of polymer grades
- Limited formability — 10/100, worse than 87% of polymer grades
- Limited ductility — 4.5%, worse than 75% of polymer grades
Vespel SP-21 properties
Typical room-temperature values for Vespel SP-21-SP-21; bars are the position among polymer grades.
Physical4
Vespel SP-21 has a density of 1.51 g/cm³ (0.0546 lb/in³), heavier than 88% of polymer grades. Its glass-transition temperature is 360°C (680 °F).
Mechanical10
Vespel SP-21 has a tensile strength of 65 MPa (9.43 ksi), stronger than 73% of polymer grades. Elongation at break is 4.5% and the elastic modulus is 3.1 GPa (0.45 Msi).
Thermal9
Vespel SP-21 is rated for continuous service to 288°C (550 °F). It conducts heat at 0.87 W/m·K (0.503 BTU/hr·ft·°F), better than 99% of polymer grades. Thermal expansion is 49 µm/m·K (27.2 µin/in·°F).
Chemical & Environmental3
Corrosion resistance is excellent (85/100), better than 65% of polymer grades. UV resistance is very good.
Sustainability3
Producing a kilogram of Vespel SP-21 takes about 290 MJ of energy and emits 15 kg of CO₂ — more than 95% of polymer grades. Typical recycled content is 0%.
Manufacturability4
Vespel SP-21's machinability is good (60/100, better than 51% of polymer grades); weldability not recommended (5/100); formability not recommended (10/100).
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. Vespel SP-21 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Vespel SP-21
Is Vespel SP-21 easy to machine?
Cut dry at high speed with light feeds using sharp carbide or PCD; the graphite filler is abrasive to tooling. Skip coolant to avoid moisture pickup, and dry parts in an inert atmosphere after machining if needed.
Can Vespel SP-21 be welded?
This thermoset polyimide cannot be melt-welded. Assemble with high-temperature epoxy or polyimide adhesives, or with mechanical fasteners.
Can Vespel SP-21 be formed, bent or molded?
Parts are direct-formed from powder, or isostatically pressed and sintered at high temperature into blanks, then machined to size. Injection moulding and extrusion are not possible.
Vespel SP-21 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 |
|---|---|---|
| graphitesolid lubricant filler, wt% | 14 – 16 | 15 |
| polyimide (PMDA/ODA) matrixthermoset aromatic polyimide, non-melting | ≥ 83 (balance) |
What surface finishes work on Vespel SP-21?
Fine grinding and lapping give high-quality sealing faces. Plating and anodizing are not applicable; dry per DuPont's recommendation before assembly and allow for moisture-related swelling.
How much does Vespel SP-21 cost?
Vespel SP-21 is a high-cost polymer ($$$$), pricier than about 78% 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.
Vespel SP-21 — frequently asked
What is Vespel SP-21 used for?
Vespel SP-21 is typically used for turbine engine seal rings, high-temperature bearings and bushings in jet engines. In short: graphite-filled Vespel; 288 °C continuous service; triple SP-1 conductivity.
What is the tensile strength of Vespel SP-21?
Vespel SP-21 has a typical tensile strength of 65 MPa (9.43 ksi) — stronger than 73% of polymer grades. Strength varies by condition: see the 5 listed tempers.
Is Vespel SP-21 easy to machine?
Reasonably — machinability is rated good (60/100, better than 51% of polymer grades). Cut dry at high speed with light feeds using sharp carbide or PCD; the graphite filler is abrasive to tooling. Skip coolant to avoid moisture pickup, and dry parts in an inert atmosphere after machining if needed.
Can Vespel SP-21 be welded?
Not readily — weldability is rated not recommended (5/100). This thermoset polyimide cannot be melt-welded. Assemble with high-temperature epoxy or polyimide adhesives, or with mechanical fasteners.
What surface finishes work on Vespel SP-21?
Fine grinding and lapping give high-quality sealing faces. Plating and anodizing are not applicable; dry per DuPont's recommendation before assembly and allow for moisture-related swelling.
Can Vespel SP-21 be formed, bent or molded?
Parts are direct-formed from powder, or isostatically pressed and sintered at high temperature into blanks, then machined to size. Injection moulding and extrusion are not possible.
What is the maximum service temperature of Vespel SP-21?
Vespel SP-21 is rated for continuous use to about 288°C (550 °F), and briefly to 482°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does Vespel SP-21 cost?
Vespel SP-21 is a high-cost polymer ($$$$), pricier than about 78% 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.
Sources
- Vespel SP Polyimide Parts and Shapes — Design Handbook & Property Data — DuPont (2021)
- Vespel SP-21 / SP-211 / SP-22 grade data sheets — DuPont (Rogers Corporation Vespel business) (2023)
- MatWeb polyimide (graphite-filled) typical property listings — MatWeb LLC (2024)
- Engineering Plastics — Engineered Materials Handbook Vol. 2 (polyimides) — 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.