PTFE with 25% glass fiber
Glass-filled PTFE: less creep and wear, keeping its chemical resistance
Milled glass fiber (usually 15 to 25%) is the most common PTFE filler: it reduces cold flow (creep) and wear and keeps almost all of the material's chemical resistance, except in hydrofluoric acid and hot strong bases, which attack the glass. It is used in valve seats, loaded gaskets, piston rings and seals.
Designations and equivalents
| System | Designation |
|---|---|
| Abbreviation (ISO 1043) | PTFE + 25% glass |
| Trade names | Fibracon PTFE + 25% Glass (Roechling); POLYFLON 25GL (Daikin, compound) |
Standards by product form
| Form | Standard |
|---|---|
| Filled PTFE compound | ASTM D4745* |
| Molded rod, tube and sheet | Stock-shape manufacturer's specification |
| Food contact | Available in specific grades; confirm the lot declaration |
| Machined part to drawing | ISO 2768 tolerance or as per drawing |
Composition and filler
Nominal composition by mass
| Component | Content |
|---|---|
| PTFE | 75% |
| Milled glass fiber | 25% by mass |
Mechanical properties
Typical values from the stock-shape manufacturer's catalog, 23 °C; ISO/ASTM methods as per the source
| Property | Value |
|---|---|
| Tensile strength | 18 MPa |
| Elongation at break | 200% |
| Compressive strength | 7 MPa |
| Hardness | Shore D 64 |
Typical physical and thermal properties
| Property | Value |
|---|---|
| Density | 2.24 g/cm³ |
| Maximum continuous service temperature | 260 °C |
| Minimum service temperature | -200 °C |
| HDT (1.8 MPa) | 65 °C |
| Melting point or glass transition | 327 °C |
| Linear thermal expansion | 100 µm/m·K |
| Thermal conductivity | 0.43 W/m·K |
| Water absorption (24 h) | 0.02% |
| Dielectric strength | 13 kV/mm |
| Flammability (UL 94) | V-0 |
Calculate the weight of PTFE with 25% glass fiber bar, plate or pipe →
Friction, wear and PV limit
| Property | Value |
|---|---|
| Dynamic coefficient of friction against steel | 0.07 (dynamic, 0.8 m/s, 1 MPa, against stainless steel Ra 0.5 µm) |
| PV limit (pressure × velocity) | 0.365 MPa·m/s (at 0.05 m/s); 0.475 MPa·m/s (at 0.5 m/s); 0.59 MPa·m/s (at 5 m/s) |
| Deformation under load (creep) | 9.5% (total deformation under 14 MPa, 24 h, parallel (ASTM D621)) |
PV and friction depend on the test method, the mating surface (steel, stainless, roughness), lubrication and each manufacturer's safety factor: compare values from the same source and confirm by testing in critical applications.
Chemical resistance
| Medium | Resistance |
|---|---|
| Acids | Good, except hydrofluoric acid (attacks the glass) |
| Bases (alkalis) | Limited: alkalis attack the glass fiber |
| Solvents | Excellent |
| Hydrocarbons and oils | Excellent |
| Steam and hot water | Good, but water can cause uneven wear |
Compare PTFE with 25% glass fiber with the other plastics by application, temperature and medium →
Stock forms and sizes
- Rod (round bar)
- Sheet (plate)
- Tube and bushing
- Molded bushings
- Raw material: rod (round bar), sheet (plate) and tube, cut to size
- Machined part to drawing or sample, in the same order as the metal parts
- Lot certificate of conformity; FDA/EU 10/2011 declaration when the grade allows
Service temperature, machining and assembly
| Item | Usual practice |
|---|---|
| Service temperature | Continuous service up to 260 °C; minimum -200 °C (unloaded; under load, limited by HDT and creep). |
| Annealing (stress relief) | Stress-relief annealing before precision machining. |
| Bonding and welding | Cannot be welded; bonding only after chemical etching of the surface. |
| Machining | Glass is abrasive: use carbide or diamond (PCD) tooling and moderate speeds. |
Typical applications
- Valve seats
- Loaded gaskets and seals
- Compressor piston rings
- Bushings and slide plates in chemical media
- Insulators under mechanical load
Alternatives: Carbon-filled PTFE in water, steam and alkaline media; bronze-filled PTFE in oil hydraulics; PEEK for high load and temperature.
Frequently asked questions
Which standards cover PTFE with 25% glass fiber?
Filled PTFE compound: ASTM D4745*. Molded rod, tube and sheet: Stock-shape manufacturer's specification. Food contact: Available in specific grades; confirm the lot declaration. Machined part to drawing: ISO 2768 tolerance or as per drawing.
Up to what temperature can PTFE with 25% glass fiber be used?
Continuous service up to 260 °C; minimum -200 °C (unloaded; under load, limited by HDT and creep).
Which materials can replace PTFE with 25% glass fiber?
Carbon-filled PTFE in water, steam and alkaline media; bronze-filled PTFE in oil hydraulics; PEEK for high load and temperature.
Does glass fiber score the shaft?
It can score soft shafts. Against untreated steel or in water, prefer carbon- or graphite-filled PTFE, which is less abrasive.
When should glass-filled PTFE be used instead of virgin PTFE?
When the part carries a constant load (valve seat, tightened gasket, piston ring): glass reduces creep and wear with little loss of chemical resistance.
