1. PPS (Polyphenylene Sulfide)
PPS is arguably the “best value” for continuous Skydrol immersion. In the industrial world, it’s often used as a replacement for high-end alloys and expensive fluoropolymers.
- The Skydrol Advantage: PPS is almost entirely inert. It has no known solvents below 200°C. In Skydrol immersion tests, PPS shows zero measurable swelling or loss of tensile strength.
- Mechanical Profile: It is naturally flame-retardant and extremely stiff. However, it can be more brittle than PA12-CF.
- 3D Printing Reality: It requires a heated chamber (90°C+) and high nozzle temperatures (320°C+), but it is generally easier to print than PEEK.
2. PEEK & PEKK (The PAEK Family)
These are the “top-tier” aerospace plastics used for flight-critical fluid manifolds.
- The Skydrol Advantage: The ether-ketone bonds in PEEK are fundamentally resistant to the solvent action of phosphate esters. It is the standard for commercial jet fuel and hydraulic connectors.
- Mechanical Profile: PEEK offers the highest tensile strength of any 3D-printed polymer (approaching the strength of some aluminum alloys) and remains stable up to 250°C.
- 3D Printing Reality: Extremely difficult to print. You need an industrial machine capable of 400°C+ nozzle temps and a 150°C+ active heated chamber to prevent the part from delaminating or warping.
3. PEI (Ultem 9085 / 1010)
Ultem is the most “certified” material in aerospace (meeting FST — Flame, Smoke, and Toxicity standards).
- The Skydrol Advantage: While Ultem 9085 is rated for Skydrol exposure, it is an amorphous polymer. This means it is more susceptible to “environmental stress cracking” than semi-crystalline materials like PPS or PEEK if the part is under high mechanical load while submerged.
- Mechanical Profile: Excellent strength-to-weight ratio and extremely predictable behavior in aerospace environments.
- 3D Printing Reality: Requires high-temperature hardware, but because it is amorphous, it is very dimensionally stable (less warping than PEEK).
| Material | Immersion Rating | Printing Difficulty | Best Use Case |
| PPS | Superior | Moderate/High | High-pressure manifolds; chemical pumps. |
| PEEK | Superior | Extreme | Flight-critical structural fluid connectors. |
| PEI (Ultem) | Good | High | Interior aerospace brackets and ducting. |
| PA12-CF | Intermittent | Moderate | Tooling, jigs, and temporary fluid covers. |
The “Hidden” Factor: Crystallinity. > Semi-crystalline materials (PPS, PEEK) perform better in immersion than amorphous materials (Ultem) because their molecular chains are packed so tightly that the Skydrol molecules literally cannot find space to penetrate the polymer matrix.