Material Selection Decision Tree: PEEK vs PTFE vs PI vs PSU
Choosing the right high-performance plastic is the difference between a part that runs for a decade and one that fails in a week. When the candidate list narrows to PEEK, PTFE, polyimide (PI), and polysulfone (PSU), the decision often feels overwhelming because each material is capable in different ways. This guide replaces guesswork with an operational decision tree — a step-by-step flow you can follow for any application, plus scenario-by-scenario recommended selections grounded in verified data.
1. The Four Materials, Briefly
| Material | Continuous temp | Key strength | Key limitation |
|---|---|---|---|
| --- | --- | --- | --- |
| PEEK | ~260 °C | Strength + hydrolysis resistance + broad chemical + processability | Cost; lower stiffness than metal |
| PTFE | -260 to +260 °C | Near-total inertness, lowest friction | Mechanically weak, creeps |
| PI (polyimide, LY-601) | ~360 °C (dry) | Extreme heat, low wear, radiation | Cost, poor hydrolysis, harder to process |
| PSU (polysulfone) | ~150–180 °C | Low cost, good hydrolysis/steam resistance, transparent | Lower continuous temperature, lower strength |
Sources: Victrex® / Evonik PEEK and PSU datasheets; PTFE industry data; LY-601 measured PI data (UL 746B, ISO methods).
2. The Decision Tree: Step by Step
Follow these questions in order. Each answer eliminates materials until one (or a primary/secondary pair) remains.
Step 1 — What is the peak continuous operating temperature?
- Below ~150 °C, cost-sensitive, general service → consider PSU (lowest cost of the four; good hydrolysis/steam resistance)
- Below ~260 °C → PEEK, PTFE remain candidates
- Above ~260–300 °C, dry service → PI (LY-601) is the answer
- Above ~260 °C but wet/steam → neither PI nor PEEK fully; re-evaluate (PI hydrolyses, PEEK limited) — often a coated metal/ceramic or careful PEEK grade
Step 2 — Is the part load-bearing, or a seal/insulator?
- Structural / load-bearing / creep-critical → PEEK (or PI if >300 °C dry)
- Pure sealing / gasket / insulator where inertness or low friction dominates → PTFE, backed by a PEEK/PI structural part if loaded
Step 3 — What is the media?
- Aggressive chemicals, strong bases/acids → PTFE (near-total inertness) or PEEK (if structural)
- Electrolyzer KOH / PEM acidic → PEEK (frames/back-up) + PTFE (gaskets)
- Hot water / steam → PEEK (hydrolysis); avoid PI; PSU also resists steam/hydrolysis at lower temperatures
Step 4 — Does the part move, slide, or wear?
- Lowest friction needed → PTFE
- Low wear + strength in dynamic parts → PEEK / CFR-PEEK (or PI at very high temp)
Step 5 — What is the production volume?
- Low-to-mid / prototype → CNC-machined PEEK (no tooling)
- High volume → injection-moulded PEEK or, for inert gaskets, PTFE
- Near-net large shapes → compression moulding
3. The Tree as a Visual Table
| If you need… | → Choose |
|---|---|
| --- | --- |
| Low cost, steam/hydrolysis resistant, <~150–180 °C | PSU |
| Strength + hydrolysis + broad chemical, <~260 °C | PEEK |
| Inertness + lowest friction, sealing/insulating | PTFE |
| Extreme dry heat to ~360 °C, low wear | PI (LY-601) |
| Structural seal under bolt load | PEEK back-up + PTFE gasket |
| Electrolyzer frame/back-up ring | PEEK (GF for stiffness) |
| Ultra-high-temperature dry wear | PI (LY-601) |
| High-volume complex 3D part | Injection-moulded PEEK |
4. Scenario-by-Scenario Recommended Selection
Scenario A: Sealing gasket in an electrolyzer
Recommendation: PTFE primary gasket + PEEK back-up ring/frame.
- PTFE gives inertness and low friction against the KOH/acidic media; PEEK back-up resists creep and provides structural support. A proven two-material stack.
Scenario B: Pump/actuator wear ring, <260 °C, feeding abrasive or chemical media
Recommendation: CFR-PEEK (e.g., LY-205, measured friction ~0.13, very low wear volume).
- Strength, low wear, and chemical resistance beat PTFE's creep and PSU's temperature limitation.
Scenario C: High-temperature dry seal in an exhaust / furnace-adjacent joint, >300 °C
Recommendation: PI (LY-601), continuous ~360 °C.
- No other material in the four survives sustained dry heat this high; its low wear keeps it alive.
Scenario D: Medical / food-adjacent or hydrolysis-critical part below ~150 °C
Recommendation: PSU or PEEK (depending on strength need).
- PSU is economical and steam-resistant; PEEK where more strength is needed, with ISO 13485 quality support.
Scenario E: Electrolyzer structural frame needing high stiffness at low weight
Recommendation: Glass-fibre-filled PEEK (LY-200 series, HDT >280 °C).
- Fibre-filled PEEK is ~70 % lighter than a titanium frame and provides stiffness with insulation and corrosion resistance.
5. Common Selection Mistakes
- Temperature-only thinking — the number rarely tells the full load/wet/cycling story.
- Picking the "highest rated" material (e.g., PI everywhere) when cost and hydrolysis sensitivity argue otherwise.
- Cloning a metal part in plastic — design for the polymer's modulus/CTE, don't just swap materials.
- Using PTFE where structural strength is needed — pair it with PEEK/PI structure.
- Ignoring processing economics — a great material is useless if the volume can't justify its processing route.
- Skipping the official datasheet and service-condition validation.
6. Specification Checklist
- [ ] Peak + continuous temperature defined (separate loaded vs unloaded)
- [ ] Pressure / load / creep driving forces identified
- [ ] Media + hydrolysis compatibility confirmed for the exact service
- [ ] Wear/friction need (static vs dynamic) quantified
- [ ] Volume and processing economics decided upfront
- [ ] Grade datasheet (ISO/ASTM) obtained; traceability confirmed
- [ ] ISO 9001 / ISO 13485 quality system in place
- [ ] Prototype + test evidence for compression/leakage/wear at service conditions
7. Final Decision Summary
Step through the tree and you'll almost always land cleanly:
- ≤ ~180 °C, cost + steam, non-structural: PSU
- ≤ ~260 °C, structural/load-bearing/hydrolysis, or a back-up for PTFE: PEEK
- Inert, low-friction sealing/insulating role: PTFE (paired with PEEK/PI structure when loaded)
- > ~260–300 °C dry, low-wear: PI (LY-601)
Match the material to the operating condition, not to a datasheet trend, and confirm every choice against the official grade datasheet before you commit.
Frequently Asked Questions
- What is the difference between PSU and PEEK? PSU is lower cost and has good steam/hydrolysis resistance but only to ~150–180 °C and less strength; PEEK is stronger, hydrolytically and chemically robust, and reaches ~260 °C continuous.
- Can I use PSU instead of PEEK to save cost? Only if your temperature is ≤ ~150–180 °C and loads are modest. Above that, or where strength/creep matters, PEEK is the right investment.
- For an electrolyzer, should frames be PEEK and gaskets be PTFE? Yes — this is the proven architecture: PTFE gaskets for inert primary sealing, PEEK (fibre-filled where stiff) for the load-bearing, insulating frame.
Related Topics
- PEEK vs PTFE vs Polyimide for Sealing: Which Material, When?
- PEEK vs Metals: When Does a Polymer Part Beat Steel or Titanium?
- PEEK Properties: A Complete Engineering Guide
Dalian Luyang Technology Development Co., Ltd. (www.newmaterialchina.com) manufactures PEEK, PI, and PTFE precision parts — seals, inserts, machined components, and electrolyser frames — under ISO 9001 and ISO 13485. Established 2006. Contact: liyulong@luyangkeji.com · WhatsApp +86 15989781752. This guide is educational reference material; always verify against your chosen grade's official datasheet.