Engineers and buyers in pneumatics rarely have the luxury of perfect routing and steady ambient conditions. Real plants have tight machine envelopes, moving axes, vibration, oil carryover in compressed air, and seasonal swings in temperature and humidity. In that reality, the “PU vs. PA (nylon)” decision isn’t academic—it directly impacts leak rates, fatigue failures, maintenance time, and safety margins on pressure.
I choose polyurethane when flexibility, tight bend radius, dynamic motion, and cold performance matter; I choose nylon when I need higher working and burst pressure, better high‑temperature tolerance, and stronger chemical resistance to hydrocarbons. Temperature and humidity swing the decision: PU stays supple and resists kinking in the cold, while nylon keeps its shape and pressure rating in the heat and handles lubricated air better. For small bend radii and push‑to‑connect reliability, PU wins; for main trunks and hot zones, nylon wins. Reinforcement (braid or multi‑layer) pushes both materials into demanding duty cycles—use reinforced PA for high pressure/heat, reinforced PU for aggressive flex and abrasion.
Let me break the trade‑offs into practical selection criteria: pressure vs. flexibility, ambient heat vs. cold starts, humidity and oil exposure, bend radius in cramped layouts, and when to step up to reinforced constructions for duty cycles that punish standard tubing.
Comparison Table: Polyurethane (PU) vs. Nylon (PA) Tubing
| Factor | Polyurethane (PU) | Nylon (PA) | My Take for B2B Pneumatics |
|---|---|---|---|
| Flexibility & Bend Radius | Very high flexibility; tight radii with low kink memory | Stiffer; larger minimum bend radius | PU for tight routing, dress‑packs on robots, and dynamic carriers |
| Abrasion & Wear | Excellent abrasion resistance; good impact absorption | Excellent abrasion; higher tensile strength | Both are tough; PU better for repeated contact + vibration; PA for sliding wear over edges |
| Working Pressure (typ. 1/4 in OD) | ~105–150 psi (derates with heat) | ~200–300 psi (more stable vs. heat) | PA for main air trunks/high pressure; PU for tool drops and motion axes |
| Burst Pressure | Lower than PA at same wall | Higher; better safety margin | Safety‑critical circuits favor PA |
| Temperature Range | Cold‑friendly; stays flexible in low temps; softens earlier in heat | Wider high‑temp capability; dimensionally stable | Cold rooms: PU; hot zones/near ovens: PA |
| Humidity & Moisture | Can absorb more moisture; slight dimensional shift | Lower moisture uptake; stable sizing | High humidity precision pneumatics: PA backbones |
| Chemical Resistance | Good overall; may swell with some hydrocarbons/solvents | Stronger vs. hydrocarbons, fuels, many lubricants | Oil‑laden compressed air: PA generally better |
| Push‑to‑Connect sealing | Softer wall seals well; fewer micro‑leaks | Rigid wall; cleaner straight runs; depends on fitting tolerances | PU improves seal reliability; PA looks crisp in panel builds |
| Vacuum Service | Up to ~28 inHg typical | Up to ~28 inHg typical | No major difference for standard pneumatics |
| Cost & Installation | Higher material cost; lower install labor (fewer fittings) | Often 20–30% less; more elbows/fittings required | Total cost depends on layout complexity |
| Transparency | Transparent grades common | Typically opaque | PU helps visual flow/contamination checks |
| Certifications | FDA/medical grades available (formulation‑specific) | SAE J844 for air brake (PA only) | Industry compliance may decide the material |
What trade-offs do I face in flexibility, abrasion resistance, and pressure rating?
Flexibility and Bend Radius
- Based on what I’ve seen on robot dress‑packs and tight machine guards, PU’s elasticity is a real install-time advantage. You can meet tight bend radii without kinking, and PU has low “memory,” so it doesn’t fight the route.
- Nylon’s stiffness makes it better for straight, panel‑to‑manifold runs. If you try to force tight bends with PA, you end up adding elbows, which add leakage points and assembly time.
Practical guideline
- If your minimum bend radius is close to the tubing OD (compact routing), go PU.
- If your layout allows generous bends and you want crisp, straight runs with higher pressure margins, go PA.
Abrasion and dynamic wear
- PU resists abrasive scuffing very well and absorbs impact. In mobile machinery or EOAT (end‑of‑arm tooling), PU reduces stress at fittings during motion cycles.
- PA has higher tensile strength and handles sliding abrasion over long runs—think cable tracks and places with repetitive rubbing against surfaces.
Practical guideline
- For vibration, frequent flexing, and contact with machine edges, I default to PU unless the environment involves continuous sliding wear; then PA can be a better long‑term choice.
Pressure rating and burst strength
- Nylon consistently carries higher working and burst pressures at the same wall thickness and derates less with temperature rise.
- PU works great for typical shop air drop lines and valve islands but isn’t my pick for high‑pressure headers or circuits with frequent spikes.
Practical guideline
- Main air trunks, safety‑critical actuators, or pressure above ~200 psi: choose PA.
- Tool drops, motion axes, and short flexible whips: PU is sufficient and easier to install.
How does temperature and humidity affect PU vs. PA in my plant?
High temperatures
- Nylon maintains dimensional stability and pressure capacity across a wider high‑temperature range. Near ovens, dryers, or hot manifolds, PA resists softening and creep better.
- PU will soften earlier, and pressure ratings derate more quickly with heat.
Low temperatures
- PU stays flexible in the cold and resists kinking or cracking during cold starts—useful in refrigerated spaces or winter startups.
- PA can get rigid in cold environments, increasing the chance of stress at fittings and kink risk if bent aggressively.
Humidity and moisture uptake
- PA absorbs less moisture and holds tighter dimensions, which matters for precise push‑to‑connect tolerances and long panel runs in humid plants.
- PU can take on more moisture over time, slightly affecting fit and dimensions. Not usually catastrophic, but it can show up as intermittent leaks in marginal fittings.
Decision cues I use on site
- Hot zones or continuous elevated temperature: PA.
- Cold rooms, frequent thermal cycling, or outdoor winter operation: PU.
- High humidity with lots of push‑to‑connects and long straight runs: PA.
Which material handles tight bending radii better in my machine layout?
Tight radius and routing complexity
- PU is the clear winner for tight radius routing, cable tracks, and around brackets or guards. You’ll need fewer elbows and tees, reducing leak risk and installation time.
- PA can be forced into tighter paths, but it will fight the bend and may stress fittings. Over time, this leads to micro‑leaks or tube creep at connections.
Push‑to‑connect reliability
- PU’s softer wall forms a better seal in push‑to‑connect fittings, especially if alignment is imperfect. In dense valve manifolds, this cuts debug time.
- PA’s rigidity delivers picture‑perfect straight runs, which some panel builders prefer, but sealing depends more on exact cut quality and tolerances.
My rule of thumb
- If you’re staring at a machine with minimal clearance and multiple moving axes, choose PU.
- If the panel is open, runs are long and straight, and pressure margins matter, go PA.
When should I choose reinforced PA or PU for demanding duty cycles?
What “reinforced” buys you
- Reinforced PU (braided or multi‑layer): increases working pressure and crush resistance while maintaining superior flexibility. Good for aggressive motion cycles with occasional pressure spikes.
- Reinforced PA (braided/multi‑layer): pushes pressure capability higher and improves high‑temperature stability and fatigue resistance. Ideal for hot, high‑pressure pneumatic lines and environments with oil/fuel exposure.
Use cases I recommend reinforcement
- Rapid cycling actuators with pressure surges or hammering: reinforced PU if routing is tight and motion is continuous; reinforced PA if pressure peaks are high and the area runs hot.
- Harsh mechanical environments (forklifts, mobile equipment, stamping areas): reinforced PU for impact and bend performance; reinforced PA when abrasion + pressure + heat combine.
- Oil‑rich compressed air or exposure to hydrocarbons: reinforced PA generally outlasts PU.
Integration tip
- Hybrid systems work best: PA (reinforced if needed) for main distribution and manifolds; PU (reinforced if needed) for flexible whips into tooling and axes.
Conclusion
From an engineering and procurement standpoint, the PU vs. PA decision hinges on four levers: flexibility, pressure, temperature, and environment. I specify polyurethane when the layout is tight, motion is frequent, and low temperatures are part of the job—its bend radius, impact absorption, and sealing in push‑to‑connects reduce assembly time and maintenance. I specify nylon when pressure margins, high‑temperature resilience, dimensional stability, and hydrocarbon resistance drive reliability—its higher working/burst ratings and stability make it the right backbone material. For demanding duty cycles, reinforcement extends both materials into tougher territory: reinforced PU for dynamic, tight‑bend applications; reinforced PA for hot, high‑pressure, chemically challenging lines. If in doubt, split the system: nylon for trunks, polyurethane for flexible connections.
FAQ
What’s the typical working pressure difference at 1/4 inch OD?
- PU commonly runs ~105–150 psi at room temperature; PA often runs ~200–300 psi. Both derate with heat, but PU derates more.
Does PU or PA seal better in push‑to‑connect fittings?
- PU’s softer wall usually seals better, especially with minor misalignment or cut imperfections. PA seals well when cuts are clean and tolerances are tight.
Which material is better in oil‑lubricated compressed air?
- Nylon generally tolerates lubricants and hydrocarbons better over the long term. PU performance depends on formulation; check manufacturer compatibility.
Are there FDA or potable water grades?
- Yes for PU—many formulations offer FDA/USP compliance. Nylon may have food‑contact grades but is less common; verify certifications per application.
How do I handle very small bend radii without kinks?
- Use PU, consider smaller OD, and avoid sharp entry angles at fittings. For extreme bends under load, use reinforced PU to resist collapse.
Can I run either material under vacuum?
- For standard pneumatic vacuum (to ~28 inHg), both PU and PA are suitable. Verify wall thickness for collapse resistance in larger diameters.
Quick Application Guide
| Application Scenario | Recommended Material | Reasoning |
|---|---|---|
| Main compressed air header (≥200 psi), warm ambient | Nylon (reinforced if needed) | Higher pressure and temperature stability |
| Robot dress‑pack, tight routing, cold starts | Polyurethane (possibly reinforced) | Flexibility, bend radius, cold performance |
| Oil‑laden air, petrochemical exposure | Nylon | Better hydrocarbon resistance |
| Food/beverage line with visual flow | FDA‑grade transparent PU | Compliance + transparency |
| Panel builds with long straight runs | Nylon | Dimensional stability and crisp routing |
| Mobile machinery with vibration | Polyurethane (reinforced in harsh duty) | Impact absorption and fitting stress reduction |
