Grades / Unfilled PEEK
Unfilled PEEK, the grade that takes the steam
Unfilled PEEK is the default when a part has to be tough, survive steam or sit in chemicals. It is also the grade that moves most with temperature, which is why the fits on a hot part need calculating rather than copying from a metal drawing.
Unfilled PEEK against the other grades
Typical published values. The full matrix, with what each row changes, is on the property data page.
| Property | Unit | Unfilled PEEK | Unfilled | GF30 | CF30 | Bearing |
|---|---|---|---|---|---|---|
| Density | g/cm³ | 1.30 - 1.32 | 1.30 - 1.32 | 1.49 - 1.51 | 1.40 - 1.44 | 1.44 - 1.46 |
| Tensile strength | MPa | 90 - 100 | 90 - 100 | 150 - 170 | 130 - 140 | 90 - 110 |
| Tensile modulus | GPa | 3.5 - 4.0 | 3.5 - 4.0 | 9 - 11 | 12 - 14 | 7 - 9 |
| Coefficient of friction, dry against steel | µ | 0.30 - 0.40 | 0.30 - 0.40 | 0.35 - 0.45 | 0.20 - 0.30 | 0.10 - 0.20 |
| Thermal expansion, below Tg | µm/m·K | 45 - 50 | 45 - 50 | 20 - 24 | 14 - 18 | 18 - 24 |
| Thermal conductivity | W/m·K | 0.25 | 0.25 | 0.40 - 0.45 | 0.85 - 0.95 | 0.6 - 0.9 |
| Volume resistivity | Ω·cm | > 10¹⁵ | > 10¹⁵ | > 10¹⁵ | 10³ - 10⁶ | 10³ - 10⁶ |
| Tolerance a shop quotes | mm | ±0.05 | ±0.05 | ±0.05 | ±0.025 | ±0.05 |
Choose it when
- Repeated sterilisationHundreds of autoclave cycles at 134 °C without losing strength, where PEI and polysulfone hydrolyse.
- Impact and handlingElongation of 20 to 45% against 2 to 3% for filled grades. A dropped instrument survives.
- Chemicals and hot waterStable in almost everything short of concentrated sulfuric and strong oxidising acids.
- Electrical insulationVolume resistivity above 10¹⁵ Ω·cm, so it insulates where carbon filled cannot.
- Sealing facesTakes a finer finish than filled grades because there are no fibre ends at the surface.
Look elsewhere when
- Loaded and hotCreep sets the limit above Tg. A part carrying load at 150 °C and above wants GF30.
- Tight fits at temperatureExpansion of about 47 µm/m·K is the highest of the family, four times steel.
- Sliding surfacesDry friction of 0.30 to 0.40 against steel. A bearing grade is the right answer.
- Stiffness driven partsAt 3.5 to 4.0 GPa it is about one fiftieth as stiff as steel. Grow the section or filter to a filled grade.
What changes in the shop
What a shop prices differently for this grade, and what that means for your drawing.
Fit calculator and annealing calculator both use these numbers.
- Easiest of the family to cutSharp polished tooling, positive rake, and it does not eat edges the way fibre filled stock does.
- Heat has nowhere to goThermal conductivity of 0.25 W/m·K, so chip evacuation and coolant matter more than cutting speed.
- Stress relief on thin partsRough, anneal, finish once walls drop under about 3 mm or a bore is tighter than ±0.05 mm.
- Tolerance±0.05 mm is the number a shop quotes without a conversation. Tighter needs annealed stock and a stated inspection temperature.
Typical parts
Where this grade turns up in practice.
- Surgical instrument handles and guides
- Sterilisation tray components
- Pump and valve parts in hot chemicals
- Analytical fluid path fittings
- Insulating washers, bushings and standoffs
- Food and pharma contact parts
Questions about Unfilled PEEK
More in the full question list.
Is unfilled PEEK strong enough to replace metal?
For load it often is, at 90 to 100 MPa. For stiffness it is not, at 3.5 to 4.0 GPa against 69 for aluminium and 200 for steel. Most failed conversions are stiffness, not strength.
What colour is unfilled PEEK?
Natural is a light beige or tan. Black is the same polymer with carbon black pigment, which is not the same thing as carbon fibre filled and does not make it conductive.
Can unfilled PEEK be used for implants?
Implant grade stock exists, supplied to ASTM F2026 with lot traceability and documented biocompatibility testing. It behaves like ordinary unfilled PEEK on the machine. The document chain is what you are buying.