Comparisons / PTFE
PEEK vs PTFE
PTFE survives chemicals nothing else does and reaches a slightly higher continuous temperature. It also deforms under a load you would not think twice about. That single trade decides almost every case.
| Property | Unit | PEEK | PTFE |
|---|---|---|---|
| Continuous service temperature | °C | 250 | 260 |
| Tensile strength | MPa | 90 - 100 | 20 - 30 |
| Tensile modulus | GPa | 3.5 - 4.0 | 0.4 - 0.6 |
| Thermal expansion | µm/m·K | 47 | 100 - 160 |
| Coefficient of friction | µ, dry vs steel | 0.30 - 0.40 | 0.05 - 0.10 |
| Water absorption | % at 24 h | 0.1 | < 0.01 |
| Relative stock price | acetal = 1 | 10 | 3 |
Read the modulus row twice. PTFE is roughly one seventh as stiff as PEEK, which is why a PTFE part under sustained load keeps moving long after it was installed.
Dry running capacity, where the two part company
Choose PTFE when
- The media attacks PEEK: concentrated sulfuric acid, strong oxidising acids, some mixed acid systems
- Friction is the whole job and there is almost no load, such as a static seal, a slide pad or a low speed guide
- The part is a gasket, a liner or a diaphragm where deformation is the function rather than the failure
- Budget matters and the part sees no meaningful stress
Choose PEEK when
- Anything is loaded while hot, which is where PTFE creep ends the argument
- A dimension has to hold. PTFE expansion is two to three times PEEK and it moves with clamping pressure too
- The part is machined to a real tolerance and inspected against it
- Steam, pressure and repeated cycles are involved
- The part slides under load, where a bearing grade PEEK carries far more PV
What it costs in practice
PTFE stock runs around a third of the price of PEEK per kilo, and its density is higher, so the gap by volume narrows. The saving is real but smaller than the headline.
Where PTFE gets expensive is scrap and rework. A part machined to ±0.05 mm in PTFE often measures differently an hour later or once it is clamped in the assembly, so shops quote wider tolerances or add inspection. On a precision part the cheaper material can end up costing more per good piece.
- Seal backup ringPTFE seals, PEEK backs it up. The two work together rather than competing, which is the most common arrangement in high pressure service.
- Valve seatPTFE below moderate pressure, PEEK where the seat has to hold shape under load and temperature.
- Dry bushingFilled PTFE at low speed and load, bearing grade PEEK once PV rises.
- Chemical line fittingPTFE if the acid is aggressive, PEEK if the fitting is threaded, pressurised or has to hold a tolerance.
Questions people ask
Is PTFE better than PEEK for chemical resistance?
At the extremes, yes. PTFE handles concentrated sulfuric and strong oxidising acids that attack PEEK. For everything short of that, both survive, and the decision moves to whether the part carries load.
Can PTFE replace PEEK in a bushing?
Only at very low load. PTFE has a tensile strength around 20 to 30 MPa and creeps under almost any sustained load, so a filled PTFE or a bearing grade PEEK is the usual answer where the bushing actually carries something.
Which is easier to machine?
Neither is hard, both are unforgiving in different ways. PTFE is soft and moves under clamping pressure and with temperature, so holding a tolerance is the problem. PEEK holds size but punishes dull tooling and residual stress.