Verdict: VICTREX PEEK 90HMF20 is the grade to specify when an unfilled PEEK such as 450G is chemically and thermally right for the job but simply too flexible. The 20% carbon-fibre reinforcement roughly triples stiffness and materially raises load-bearing capability, while the low-viscosity 90-series base keeps thin walls and long flow paths mouldable. The trade-off is anisotropy and abrasiveness — this is not a drop-in substitution, and treating it as one is the single most common failure mode we see in the field.
What the grade actually is
Read the nomenclature and most of the selection question answers itself. The “90” denotes the low-viscosity injection-moulding base polymer, the “HMF” indicates high-modulus carbon fibre reinforcement, and “20” is the nominal fibre loading by weight. It sits below 90HMF40 and 150CA30 in stiffness, but above them in flow. For thin-wall connectors, small precision gears, and long-flow structural brackets, that flow advantage is often the deciding factor.
Mechanical performance in context
Datasheet-typical values place tensile strength in the low-200 MPa range and tensile modulus in the high-teens GPa, against roughly 100 MPa and 4 GPa for unfilled PEEK. In practice that reads as a genuine light-metal replacement candidate: specific stiffness competitive with cast aluminium at roughly half the density, with no galvanic corrosion and far better fatigue behaviour in wet or chlorinated environments.
Two caveats matter more than the headline numbers. First, published figures are measured on injection-moulded bars with favourable fibre alignment; a real part with ribs, gates, and weld lines will not reproduce them. Expect meaningful directional variation and design against the transverse property, not the flow-direction property. Second, elongation at break drops sharply versus unfilled PEEK. Any part relying on snap-fits, press-fits, or plastic deformation to absorb tolerance stack-up should be re-evaluated.
Thermal and environmental behaviour
Glass transition stays near 143 C and melting near 343 C, as with all PEEK grades — reinforcement does not change the polymer backbone. What it does change is heat-deflection temperature, which climbs to roughly the 300 C region because the fibre network carries load above Tg. That is the practical benefit: continuous service capability at elevated temperature under mechanical load, rather than merely surviving the temperature. Steam, hydrolysis, and hydrocarbon resistance remain excellent. Fibre-matrix interface quality, not the fibre itself, governs long-term hot-wet performance, so lot-to-lot consistency deserves attention.
Processing reality
Melt temperature typically runs 360-400 C with mould temperature at 175-205 C. The mould temperature is non-negotiable: run it cold and you get an under-crystallised part that looks acceptable, passes incoming inspection, then dimensionally shifts and loses chemical resistance in service. Post-mould annealing is advisable for tight-tolerance components.
Carbon fibre is abrasive. Budget for hardened or coated screws, barrels, and gate inserts, and expect faster tool wear than with unfilled grades. Gate placement drives fibre orientation, which drives both warpage and where the part is actually strong — treat gating as a structural decision, not a cosmetic one. Weld lines around holes and inserts are the usual crack-initiation sites.
Where it wins, where it loses
Strong fit: metal-replacement brackets and housings in aerospace and oil-and-gas, semiconductor handling components needing stiffness plus low outgassing, downhole seal support rings, thin-wall electrical connectors, and precision gears in high-temperature actuators.
Poor fit: electrically insulating applications, since carbon fibre gives partial conductivity; medical implants, where implantable grades are the correct route; food-contact parts requiring specific approvals; and thick unmachined sections where wall-thickness-driven fibre orientation is uncontrolled.
Buyer checklist
- Request the current supplier datasheet — do not source properties from distributor summaries or older revisions.
- Specify both flow-direction and transverse values in your drawing notes.
- Require lot certificates covering melt viscosity and fibre content, and lock in an alternate lot for qualification.
- Qualify on moulded parts, not plaques, and include annealed dimensional data.
- Confirm regional stock and lead time; reinforced PEEK grades carry longer replenishment cycles than 450G.
Bottom line
90HMF20 is a well-balanced, credible choice where stiffness and flow both matter. Buyers who respect the anisotropy and hold mould temperature discipline get a reliable metal-replacement material. Buyers who swap it in for unfilled PEEK on a purchase order without re-engineering the part will meet the difference in the field instead.