Selection of compressed-air tubing is governed by five verifiable parameters — working pressure relative to burst rating, temperature envelope, media and chemical compatibility, minimum bend radius versus outside diameter, and the push-in versus threaded fitting system [S2][S5].
Process engineers normally spec 6 mm, 8 mm, 10 mm, or 12 mm OD in either metric or imperial inch sizes; nylon (PA), polyurethane (PU/PU2), polyethylene (PE), and PTFE dominate the four material families on offer from Festo, SMC, RS Pro, Norgren and Legris [S5][S8][S9][S10]. Use a pneumatic tubing reference to anchor each decision.
Working Pressure, Burst Rating, and the Safety Multiple
Standard 4 mm and 6 mm nylon tubing from Festo is rated 10 bar working pressure at 20 °C, while 8 mm and 10 mm variants drop to 9 bar and 8 bar respectively on the same temperature baseline [S9]. Polyurethane from RS Pro is rated up to 10 bar across 4–12 mm OD at 20 °C, making it a direct substitute for nylon on the pressure axis alone [S10].
The OEM design rule consistently applied across the major catalogues is a 4:1 burst-to-working safety factor, meaning a 10 bar working tube should burst above 40 bar; engineers should request the burst number from the supplier rather than trust the working figure alone [S2][S9]. For vacuum and suction service on pneumatic conveyor legs, the same tube is derated because of hoop-stress reversal and the published working pressure no longer applies.
Temperature Window by Material Family
Polyurethane (PU) operates from −20 °C to +60 °C in general industrial grade, with hard-PU variants (often labelled PU2 or anti-kink) extending the upper bound to roughly +80 °C [S5][S10]. Nylon 12 (PA12) widens the envelope to −40 °C to +80 °C, which is why it dominates outdoor skid instrumentation and OEM panel builds where condensate or winter exposure is expected [S8].
Polyethylene (PE) is the cost-driven choice but is limited to roughly −10 °C to +40 °C; below the lower limit it stiffens and cracks on bend, and above the upper limit it softens enough to creep out of push-in fittings [S5][S10]. PTFE covers −60 °C to +260 °C for chemical or high-temperature duty, but its stiffness demands tight bend radii and dedicated compression fittings rather than standard push-to-connect terminations [S2][S8].
Media and Chemical Compatibility
Standard PA, PU, and PE tubing all handle dry, oil-lubricated compressed air at ISO 8573-1 Class 5 particulate and Class 5 oil — the typical air-main quality a 5–8 bar plant loop delivers to a pneumatic actuator [S5][S8]. For oil-free or medical-grade air, specify PU or PA12 with explicit food-grade or FDA compliance on the data sheet rather than the default industrial SKU [S8].
PTFE is required for aggressive media including acids, solvents, and pharmaceutical CIP fluids; nylon and polyurethane swell or embrittle in those chemistries [S2][S10].
Bend Radius, Kink Resistance, and Flexibility
The published minimum bend radius is 4× OD for flexible PU and roughly 8–10× OD for semi-rigid nylon, which is the single biggest reason a control panel builder will switch material on a tight cabinet layout [S5][S10]. Hard-PU (often dual-shore or reinforced PU2) hits 3× OD and absorbs repeated flexing on a moving pneumatic cylinder rod without whitening or splitting at the outer fibre [S8][S10].
Coiled PU hoses for hand tools or pick-and-place grippers extend up to 5× resting length and recover without permanent set, but their dynamic pressure rating drops about 30 % versus a static straight tube at the same OD [S2]. For routing around a corner inside a 200 mm panel, spec PU at 6 mm or 8 mm OD; nylon at 6 mm will kink on the same bend and the pneumatic silencer exhaust will whistle on the leak path that opens at the kink.
Fitting System: Push-to-Connect vs. Compression vs. Threaded
Push-to-connect (also called push-in or one-touch) fittings from Festo, SMC, AutomationDirect, and RS Pro are sized by tube OD and grip with a stainless collet, O-ring, and release sleeve — typical leak rate is under 10⁻³ mbar·L/s at rated pressure when the tube is cut clean and square [S5][S8][S9][S10]. The same brand family offers tube-to-tube, tube-to-thread (BSPP, BSPT, NPT, and metric M5/M7), and tube-to-barb variants within a single catalogue [S5][S10].
Compression fittings (ferrule + nut) are specified where vibration, temperature cycling, or pull-off force exceeds the push-in grip envelope — typically above +60 °C or where the tube enters a pneumatic fitting on a moving head. Threaded adapters (BSPP 1/8, 1/4, 3/8) are used at the valve port; never mix metric and imperial push-in bodies on the same tube because the grip collet geometry is not interchangeable [S2][S9].
Variant Comparison on the Five Decision Criteria
Stacking the four common materials against the duty envelope makes the trade-off visible. Polyurethane wins on bend radius and flex life, nylon wins on temperature and burst margin, polyethylene wins on unit cost, and PTFE wins on chemical and thermal extremes [S5][S8][S10].
When the duty exceeds +60 °C, the comparison collapses to PA or PTFE; when the duty is below 0 °C outdoors, PE drops out and PA12 becomes the default [S5][S8].
Who Should NOT Pick the Lowest-Cost Option
Specifiers should not default to polyethylene for any line that flexes, cycles in temperature, or sees pull-off load at the fitting — the −10 °C lower limit and the 4× OD bend radius rule make PE fail in robotics, mobile equipment, and outdoor cabinets that are common pain points at site commissioning [S5][S10].
Equally, push-to-connect fittings should not be used on PTFE tube without a manufacturer-matched ferrule system; the collet will not bite the smooth PTFE surface and the joint will creep under thermal cycling [S2][S8]. For hazardous-area MCC panel builds, route the pneumatic lines alongside the MCC panel tubing guide and apply the same fire-retardant tube spec, typically FR-PU or PA12 with UL94 V-0 rating, rather than the default industrial SKU [S1].
Standards, Sourcing, and Trackable Specifications
Manufacturers publish working pressure at 20 °C and a separate burst pressure; the 4:1 safety factor is industry convention but is not a single named standard — verify the exact number on the data sheet before stamping a drawing [S2][S9]. Dimensional conformity to ISO 14743 for push-in fittings is the baseline expectation from Festo, SMC, and AutomationDirect catalogues [S5][S8][S9].
Two trackable signals: the 90030378 S-2000A installation kit ships 40 ft. of pneumatic tubing with T-connectors, spanner wrenches, 12 bolts, and clamps as a single part number — a useful bill-of-materials reference for skid builders [S3] — and EN 10305-4 Cr6-free galvanized steel tube is the hydraulic-pneumatic crossover standard when the duty calls for metal rather than polymer [S6]. The Newport plastic tubing line is sold by the foot in clear and gray variants for low-pressure pneumatic plumbing, confirming that the by-the-foot sourcing model is alive across the major catalogues [S7].