Use TPU for a true 3D printed grommet that touches the cable, flexes during installation, or must cushion vibration and edge contact. Use PETG when the printed job is really a rigid panel insert, trim frame, or support body that should hold a crisp opening. If both jobs matter, the strongest design is often a PETG frame with a replaceable TPU contact insert.
The buyer decision is not simply soft versus strong. It is cable protection and fatigue versus panel retention and dimensional stability. A rigid ring can stay intact while abrading insulation; a soft ring can protect the cable but pull out of an undersized retention groove.
This guide uses current manufacturer references checked August 10, 2026; it does not claim hands-on wear testing. Material behavior varies by formulation, hardness, moisture, print orientation, wall layout, and geometry. A printed part is not automatically a listed strain relief, cable gland, fire-stop, electrical fitting, or ingress-rated seal.
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Quick answer: TPU for the cable, PETG for the frame
| Printed job | Best default | Failure to prove against |
|---|---|---|
| Soft edge grommet around a moving or vibrating cable | TPU | Pull-out, tearing, cable-jacket wear, heat, and fatigue. |
| Rigid panel bezel or pass-through frame | PETG | Cracking during snap-in, sharp printed edges, creep, and loose fit. |
| Rigid mount plus soft cable contact | PETG carrier plus TPU insert | Insert retention, tolerance stack, and a replaceable wear surface. |
| Mains, regulated machinery, fire barrier, or claimed IP/NEMA seal | Use an approved fitting | A filament name and home print do not establish electrical, flame, pull-out, or ingress compliance. |
First decide whether the job is a grommet, bushing, restraint, or seal
Choose filament only after naming the job. TPU is the default for low-risk edge protection where the printed part must yield around a cable. PETG is the better rigid carrier when the opening must stay aligned. If the part must resist cable pull, claim ingress protection, cross a fire barrier, or carry mains wiring, stop treating it as a filament choice and use appropriately approved hardware.
| Operating condition | Buyer decision | What must be proved |
|---|---|---|
| Repeated cable motion, vibration, or edge contact | TPU contact surface | Jacket wear, lip tearing, pull-out, heat buildup, and flex-fatigue life with the real cable path. |
| Rigid panel opening or dimensional alignment | PETG frame, often with a replaceable TPU insert | Snap strain, creep under cable side-load, panel tolerance, edge radius, and insert retention. |
| Oil, grease, cleaner, acid, alkali, or unknown chemical exposure | Exact-grade data plus a representative exposure test | Swelling, softening, cracking, mass or dimension change, cable-jacket compatibility, and retention after exposure. |
| Sealing, weather entry, cable pull, mains, machinery, or fire barrier | Use the correct approved gland, bushing, strain relief, or fire-stop | The applicable pull-out, flame, ingress, temperature, and installation requirements. A home print does not establish them. |
What current official material guidance actually supports
Polymaker's current PolyFlex TPU95 technical data identifies that exact grade as Shore 95A and reports more than three-times stretch. Its chemical table rates oils and grease as Good, weak acids and weak alkalis as Fair, and strong acids and strong alkalis as Poor. Polymaker also says these typical values are for reference and comparison, not design specifications, and that end-use performance depends on the printed part and environment. Use those facts to screen the exact spool, never to certify a grommet or infer that all TPU behaves the same way.
Prusa's current PETG guidance describes PETG as tenacious and commonly used for mechanical parts, holders, clamps, and waterproof parts because of layer adhesion; it places interior and most exterior use below 80 °C. That supports PETG as the rigid-frame lane, not as proof that a printed pass-through is waterproof, chemically compatible, or rated to 80 °C under sustained side-load. Grade, color, geometry, orientation, moisture, load, and exposure still control the finished part.
TPU vs PETG for flex, abrasion, and retention
| Decision factor | TPU | PETG |
|---|---|---|
| Cable contact | Better default when the edge must yield and cushion. | Use only with generous radii and proven low movement at the contact. |
| Panel retention | Needs a deliberate groove, flange, or compression fit so flexibility does not become pull-out. | Holds crisp snap and bezel geometry more easily, but brittle features can still crack. |
| Vibration and repeated flex | Usually the better starting point, provided the lip and cable-contact surface survive the actual cycle. | Better as the stationary carrier than the rubbing interface. |
| Dimensional stability | Hardness, walls, infill, and geometry can change the feel dramatically. | Better for a flat flange and controlled opening, within the material's heat and load limits. |
| Print process | Moisture and feed-path control matter; qualify the exact spool and printer. | Usually easier to hold sharp geometry, but stringing and overly sharp edges still need cleanup. |
Design the grommet around the failure
- Round the cable-contact path: use a generous radius and remove layer ridges or burrs that can act like a file. Soft material is not automatically abrasion-proof.
- Retain the part on both faces: a groove, split flange, or captured insert is safer than hoping friction alone survives cable pull and panel vibration.
- Match the real panel thickness: a grommet modeled for a thin sheet can buckle or walk out of a thicker panel; a rigid frame can rattle in a thinner one.
- Leave cable clearance: the opening should protect the jacket without pinching it. Compression is not a substitute for rated strain relief.
- Use a split design when connectors are already installed: prove the seam cannot open, rotate into a sharp edge, or release under pull.
- Separate jobs when necessary: a PETG carrier can own alignment and snap fit while a replaceable TPU insert owns cable contact.
If the printed part must control cable pull, bending, or anchoring away from the panel, move to the cable clips and strain-relief material guide. If the decision is about compression sealing instead of edge protection, use the gaskets and seals guide. This page owns the edge-protection and pass-through decision.
Hardness is not the whole TPU decision
Shore 95A is a common printable TPU reference, not a complete grommet specification. A thick 95A ring with many walls can feel much stiffer than a thin compliant lip from the same spool. Softer TPU may protect delicate cable better but can feed less reliably and pull out more easily. Harder or high-flow TPU may print faster but behave more like a firm insert.
Buy the spool only after deciding the contact thickness, retention geometry, cable diameter, panel thickness, and printer feed path. If wet TPU is stringing or losing surface quality, use the TPU drying-versus-storage guide; if the material is dry but the part still strings badly, use the TPU stringing diagnosis.
Run a complete pass-through proof
- Print the final material, color, hardness, wall layout, orientation, flange, and panel groove rather than a generic coupon.
- Install it in a representative panel cutout with the real panel thickness and edge finish.
- Route the actual cable or a controlled representative with the same jacket diameter and flexibility. Do not use energized wiring for an improvised test.
- Check pull-out and rotation in every direction the installed cable can load the part.
- Run a documented flex and vibration cycle that represents service, then inspect the cable jacket, printed contact surface, seam, and retaining lip under good light.
- Heat-condition the unpowered assembly only within a safe, controlled method that represents the real enclosure or panel. Remeasure fit after cooling.
- Approve the design only if cable clearance, retention, edge condition, and replacement access remain acceptable. Otherwise change material, hardness, geometry, or fitting strategy and repeat.
Safety and use limits
Use a printed grommet as a prototype or low-risk cable-management part only where that is appropriate. Do not present it as a certified substitute for a listed bushing, strain-relief fitting, cable gland, fire-stop, or sealed electrical entry. For mains wiring, building penetrations, vehicles, industrial machinery, moving harnesses, hot equipment, outdoor ingress claims, or any safety-critical installation, use approved hardware and qualified review.
A soft ring does not secure a cable against pull, and a tight ring does not prove sealing. If the job requires strain relief, add a separate approved restraint. If it requires ingress protection, use the correct gland, gasket, enclosure design, and validation path.
Common failure modes
The TPU grommet pulls out of the panel
Increase positive retention before increasing hardness: check panel thickness, groove depth, flange size, seam placement, and cable pull direction. A firmer TPU may help, but it can also reduce the cushioning you chose TPU for.
The cable jacket shows a polished or worn stripe
Stop the test. Inspect contact radius, layer ridges, burrs, cable angle, heat, vibration, and clearance. TPU can still abrade a jacket if the surface and load path are wrong.
The PETG frame cracks during snap-in
Check snap strain, notch radii, print orientation, layer bonding, and panel tolerance. If the frame only exists to protect the cable edge, replace the rigid snap with a TPU design instead of overbuilding PETG.
The pass-through needs to hold position and cushion the cable
Use a two-part design: a rigid PETG carrier with a captured TPU insert. Prove the interface and keep the TPU insert replaceable.
Final verdict
Choose TPU when the printed part is truly a grommet: it touches the cable, cushions the edge, flexes into the panel, and must tolerate movement. Choose PETG when the part is really a rigid frame: it owns the flange, opening, and alignment while cable contact is light or handled by a separate insert.
For an unfamiliar functional replacement, use the durable replacement-part material router. For another compliant contact part, compare the soft-jaw and clamp-pad guide. The best grommet is not the softest or strongest print; it is the design that protects the actual cable and stays retained under the actual operating condition.
FAQ
Is 95A TPU soft enough for a cable grommet?
Often it is a practical starting point, but geometry changes effective stiffness. Prove the exact wall thickness, lip, cable diameter, panel fit, and flex cycle instead of buying from the Shore number alone.
Can PETG protect a cable edge?
Yes in a rigid, low-movement pass-through with generous radii and proven clearance. It is not the best default when the cable rubs, vibrates, or needs a compliant contact surface.
Will a TPU grommet make the hole waterproof?
Not by assumption. A grommet can protect an edge without sealing the entry. Use the correct gland, gasket, compression geometry, enclosure design, and validation when ingress matters.
Should the grommet also provide strain relief?
Do not assume it does. Edge protection and strain relief are different jobs. Use a separate approved restraint when cable pull must be controlled.