PI (Vespel)
A polymer that does not melt, for extreme heat and vacuum
Typical values for the temper in the title
Vespel-type polyimide (DuPont) does not melt: it decomposes at a very high temperature without becoming liquid, so it is formed by pressing and sintering powder, not by injection molding. It is among the most heat-resistant polymers, with good creep, wear and radiation resistance, and very low outgassing in vacuum.
It is used for seals, rings and bearings in jet engines, semiconductor and vacuum parts, and electrical and thermal insulation at temperature. It is very expensive and hard to machine.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 90 MPa | |
| Elongation A | 7% | |
| Modulus of elasticity E | 3.1 GPa | |
| Density ρ | 1.43 g/cm³ | |
| Rockwell R hardness | 45 | |
| Machinability | 20% | relative rating in the site database |
Structure and family
| Feature | Value | Meaning |
|---|---|---|
| Type | polyimide, non-melting | extreme heat resistance |
| Forming | powder pressing and sintering | not by injection molding |
| Vacuum | very low outgassing | vacuum compatible |
Typical values per producer data sheets.
Grades and versions
In engineering polymers, the choice is between an unfilled grade, filled grades (glass or carbon fiber) and special grades (bearing, medical, food). Filler strongly changes strength, stiffness and expansion.
| Version | Properties | When to choose it |
|---|---|---|
| SP-1 (unfilled) | maximum strength and ductility, electrical insulation | structural parts and insulation |
| Graphite filled (for example SP-21) | low friction and wear | bearings and rings |
Applications
- Seals and rings in jet engines
- Semiconductor parts
- Vacuum parts
- Hot bearings and wear rings
- Electrical and thermal insulation
Fabrication
Machining
Possible, but relatively difficult (database: 20%), with sharp tools and care to avoid cracks.
Joining
Not weldable. Mechanical assembly.
Water absorption
Absorbs some water. For vacuum use, dry before assembly.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| PAI (Torlon) | 190 MPa | Not recommended | PAI: strong when hot, injection moldable · material page |
| PEEK | 100 MPa | Ultrasonic / Laser | PEEK: cheaper, for lower heat · material page |
| PTFE | 25 MPa | Sintering only | PTFE: low friction, weak · material page |
Common mistakes
Looking for an ASTM standard as for another plastic
Some sources give D5205, which is the PEI standard. For Vespel, refer to the producer data sheet.
Trying to mold or weld it
The material does not melt.
Assembling in vacuum without drying
Absorbed water is released in vacuum.
Equivalents, standards and supply
| ISO | PI |
|---|---|
| Standards | Producer specification (DuPont Vespel) |
| Forms | rod · plate · molded parts |
| Producers | DuPont Vespel · Solvay Torlon-PI |
Learn more
Values are typical for an unfilled grade (unless stated otherwise) and for comparison only. In polymers, properties depend on grade, filler, temperature, moisture and load duration. For design, rely on the producer data sheet for the specific grade. Sources: ASTM classification standards (D8033, D5205, D5204, D6394, D4067 and others), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026