PEEK against the materials it replaces
PEEK costs roughly ten times what acetal does per kilo. That is fine when the part needs it and indefensible when it does not. This is the comparison that settles it, before the grade question.
| Property | Unit | POM (acetal) | PTFE | PEI (Ultem) | PPS | PEEK | PAI (Torlon) | Aluminium 6061 |
|---|---|---|---|---|---|---|---|---|
| Continuous service temperature | °C | 90 - 100 | 260 | 170 | 200 - 220 | 250 | 250 - 260 | 150 |
| Tensile strength | MPa | 65 - 75 | 20 - 30 | 100 - 110 | 70 - 90 | 90 - 100 | 150 - 190 | 290 - 310 |
| Tensile modulus | GPa | 2.8 - 3.2 | 0.4 - 0.6 | 3.0 - 3.3 | 3.8 - 4.2 | 3.5 - 4.0 | 4.5 - 5.0 | 69 |
| Thermal expansion | µm/m·K | 100 - 120 | 100 - 160 | 50 - 56 | 50 | 47 | 30 | 23 |
| Coefficient of friction | µ, dry vs steel | 0.20 - 0.35 | 0.05 - 0.10 | 0.20 - 0.40 | 0.25 - 0.35 | 0.30 - 0.40 | 0.20 - 0.30 | 0.40 - 0.60 |
| Water absorption | % at 24 h | 0.20 - 0.25 | < 0.01 | 0.25 | 0.02 | 0.1 | 0.25 - 0.33 | 0 |
| Relative stock price | acetal = 1 | 1 | 3 | 4 | 5 | 10 | 15 | 1.5 |
Typical published values for unfilled machining grades. Price index is relative stock cost per kilo with acetal as 1, rounded hard and only useful for shortlisting. Sources and what typical means are in our editorial standards.
The one line version
POM (acetal)
Cheap, stiff and fast to machine, as long as nothing gets hot.
PTFE
Chemical resistance and the lowest friction, with no load carrying ability.
PEI (Ultem)
High temperature and transparent grades at a lower price, until steam or solvents arrive.
PPS
Chemical resistance close to PEEK at a lower price, and more brittle.
PEEK
Heat and load at the same time, plus steam and chemicals.
PAI (Torlon)
The strongest of the group hot, at a price and with a post cure that catches schedules out.
Aluminium 6061
Stiff, cheap and conductive. Everything PEEK is chosen to avoid, and everything it cannot match structurally.
Head to head
Each one covers where the cheaper material wins, where PEEK is the only answer, and the cost comparison with a worked example.
- Comparison
PEEK vs PTFE
Chemical resistance and the lowest friction, with no load carrying ability.
- Comparison
PEEK vs POM (acetal)
Cheap, stiff and fast to machine, as long as nothing gets hot.
- Comparison
PEEK vs PEI (Ultem)
High temperature and transparent grades at a lower price, until steam or solvents arrive.
- Comparison
PEEK vs aluminium
Stiff, cheap and conductive. Everything PEEK is chosen to avoid, and everything it cannot match structurally.
Four questions that pick the material
In this order. The first one that gives a hard answer usually decides it.
- How hot, under load?Above about 100 °C acetal is out. Above 170 °C PEI is out. Loaded above 143 °C, unfilled PEEK gives way to a filled grade.
- What touches it?Steam and repeated sterilisation point at PEEK. Concentrated acids point at PTFE. Nothing aggressive points at acetal.
- Does it carry load or slide?PTFE creeps under almost any sustained load. PEEK carries it. If it slides, a bearing grade beats both.
- Does it have to insulate or stay non magnetic?That is where a plastic replaces aluminium even when the numbers favour metal.