Compare cable jackets and gland seals at the surface where they touch. I first identify that cable layer, then compare its compound with the supplied seal under the expected compression, temperature, fluids and movement. PE, XLPE, PUR, TPU and TPE help describe the materials, but they describe different aspects of chemistry and structure. Reading those names correctly makes the contact comparison much more useful.
An XLPE-insulated cable, for example, may have a PE outer jacket. An outer-sheath gland seal then presses against PE. The insulation still serves its electrical purpose inside the cable, while the separate seal must maintain contact with the jacket outside it.
Key takeaways
- Locate the outer jacket, conductor insulation and gland seal as separate components.
- Read PE and PUR as polymer-family names, XLPE as cross-linked polyethylene, and TPU as thermoplastic polyurethane.
- Treat TPE as a broad elastomer category; identify the subtype and compound for a replacement.
- Compare sustained compression, recovery, temperature and fluid response at the actual contact.
- Recheck dimensions, installation and assembled sealing or retention when the cable or seal changes.
Which cable layer does the gland seal touch?
The outer jacket is the sheath surrounding the cable construction. Insulation is the material serving the electrical-insulation function around conductors or in another defined part of that construction. The gland seal is a separate part that presses against the cable layer specified by the gland design.
For an outer-sheath compression seal, I pair the jacket compound with the gland’s supplied sealing insert. Read the cable construction drawing from outside inward: outer jacket, any armour or screen, bedding, insulation and conductors as applicable. Then mark the surface contacted by each gland seal. This makes a prominent insulation designation less likely to be mistaken for the material under the sealing insert.
Some glands also seal an inner sheath or bedding, clamp armour, or use a compound barrier. Identify each of those interfaces from the product section and preparation instructions. The illustration above shows the outer-sheath contact: the green regions are the two cut faces of one surrounding ring.
A documented example appears in NIST Technical Note 2320, Section 4. One cable has PE conductor insulation and a PVC jacket. Another has XLPE insulation and a chlorosulfonated-polyethylene jacket. For gland selection, I read those jacket entries separately from the insulation entries.
Read material names as chemistry and structure
A polymer name, compound code and finished-part number each answer a different question. The name identifies a family or class. The compound code identifies the formulation, including its additives and manufacturing specification. The finished cable or seal drawing then defines the geometry that reaches the contact.
| Name | Meaning | What it tells you about the material | What to compare at the gland |
|---|---|---|---|
| PE | Polyethylene | A polymer family with different grades and compounds | The specified jacket grade, surface and response under compression |
| XLPE | Cross-linked polyethylene | Polyethylene chains connected into a network | The actual layer, compound and behavior at the required temperature |
| PUR | Polyurethane | The polyurethane family | The particular chemistry, processing class and compound |
| TPU | Thermoplastic polyurethane | A thermoplastic member of the polyurethane family | The supplied formulation, hardness basis and contact-duty properties |
| TPE | Thermoplastic elastomer | A broad class combining elastic behavior with thermoplastic processing | The chemical subtype, compound and molded seal geometry |
The IUPAC polymer terminology compendium defines the underlying network and thermoplastic-elastomer concepts. I keep chemistry and processing class separate when comparing parts. For instance, a TPU jacket belongs to the polyurethane family and also to the thermoplastic-elastomer class. A description saying only “TPE” leaves its chemical family open.
What changes between PE and XLPE?
Crosslinking joins polymer chains into a network. In XLPE, that network changes the material’s response to heating and deformation compared with an uncross-linked polyethylene structure. The NIST cable study describes its PE-insulated cable as thermoplastic and its XLPE-insulated cable as thermoset. These descriptions help identify material behavior; the cable’s declared operating limits still apply to its particular construction.
For a cable specified as “XLPE insulation, PE outer sheath,” I use the PE sheath data for the outer gland contact. The XLPE information belongs with the insulation’s electrical and thermal duty. If a gland also seals an inner layer, I identify that layer separately and compare it with the relevant inner seal.
Temperature values deserve the same care. A conductor limit, an installation-temperature range and a flexing limit describe different conditions. I compare jacket and seal behavior at the temperature of the entry, including cold handling, hot dwell and repeated heating or cooling. Our cable-and-gland temperature guide explains how to match those locations and conditions.
For PE candidates, retain the grade and any stated density classification. For XLPE, retain the compound identity and relevant manufacturing or test basis. Use the actual specimen and condition when comparing deformation data. That keeps a material value connected to the jacket or bedding that will be compressed in service.
How do PUR and TPU relate?
PUR means polyurethane, a family name. TPU means thermoplastic polyurethane and therefore gives more information about the material class. If the cable description says PUR, I identify the particular polyurethane before comparing it with a TPU alternative.
TPUs commonly combine flexible segments with harder domains. Those domains act as physical junctions, while the flexible segments contribute elastic response. In research by Javni and colleagues, changing segment composition and concentration produced different morphologies in the prepared TPUs. This explains why formulation matters within the family. For a cable jacket, compare the properties of the supplied formulation at the intended temperature and exposure.
ISO 16365-1:2025 provides a designation system for thermoplastic polyurethane elastomers. Its public scope distinguishes that designation from application-specific engineering and performance data. I use the designation to identify the material, then compare hardness, additives, conditioning and the properties needed at the entry.
Abrasion, oil resistance and hydrolysis resistance address different duties. If the jacket will move against an external support, abrasion data may matter along the cable route. At the gland, compression, fluid exposure and the permitted cable movement may be more relevant. Select the test conditions that represent each location: fluid identity, concentration, temperature and duration belong with any liquid-resistance comparison.
How specific is a TPE seal description?
A thermoplastic elastomer is an elastomeric material with a thermoreversible structure that permits thermoplastic processing. The category includes several chemical systems; TPU is one member. ISO 18064:2022 organizes thermoplastic-elastomer nomenclature by chemical composition.
When choosing an alternate for a “TPE seal,” I identify the subtype, compound and part drawing. Two black inserts with similar hardness can still have different recovery or fluid response. Their wall thickness, bore and contact shape can also produce different loading on the same cable. Compare the hardness scale and conditioning alongside the material code, then fit the correct molded part to the gland.
The seal-material selection guide for EPDM, silicone and NBR develops that separate insert-selection task. Here, the key is to keep the insert identity linked to the jacket it will compress.
Compare how cable jackets and seals deform together
A compression gland loads both the sealing insert and the cable surface. A compliant jacket can deform beneath a seal, while the seal itself can lose force or recover imperfectly after loading. The resulting contact depends on the two materials, the gland geometry and the installed compression. I therefore examine the pair at the intended service condition.
Three commonly reported behaviors answer different questions:
| Property | Meaning | What it helps explain at the contact |
|---|---|---|
| Creep | Deformation grows while stress is sustained | A jacket or seal can progressively change shape under load |
| Stress relaxation | Stress falls while deformation is held | Contact force can decrease even when the assembled position changes little |
| Compression set | Residual deformation remains after a specified compression-and-recovery test | A seal’s recovery after unloading depends on the test temperature, time and recovery period |
NIST’s polyurethane-rubber study uses stress-relaxation experiments to develop a model of creep response for its tested material. It illustrates the time dependence that makes a brief hardness reading a different measurement from sustained-load behavior.
For example, consider a hypothetical replacement jacket that is more compliant under the same installed loading. It may deform more deeply beneath the unchanged insert. After a hot dwell, the pair may also retain a different contact force. I compare the installed geometry and post-conditioning seal and retention results for that combination. The cable cold-flow guide explains the time-dependent contact mechanism in more detail.
Match exposure to the property that matters
The service history identifies which material changes matter most. A warm cleaning liquid and a brief cold splash create different exposures, even if both involve the same chemical. Likewise, a cable that moves near the entry imposes a different mechanical history from a supported fixed cable. I describe the sequence and duration at the contact before comparing candidate compounds.
| Contact condition | Material response to examine | Practical comparison |
|---|---|---|
| Cleaning liquid, oil or process chemical | Swelling, softening, extraction, cracking or other property change | Use the named fluid and concentration at the relevant temperature and duration; check the assembled function afterward |
| Sustained compression | Creep, stress relaxation and recovery | Compare time-dependent results with the installed geometry and temperature |
| Cold handling or repeated bending | Stiffness, damage or contact disturbance | Match cable temperature, bend condition, support and permitted movement at the gland |
| Heating and cooling cycles | Changing dimensions and contact loading | Check the assembly after the specified cycle sequence, including movement where it occurs |
| Outdoor service | Weathering of the particular jacket and seal compounds | Compare the supplied formulation and color under the required exposure conditions |
For liquid effects, ISO 1817:2026 evaluates vulcanized and thermoplastic rubbers by comparing properties before and after immersion. Select a method suited to the actual material. A coupon test can reveal a change in swelling or mechanical properties; the installed test then shows its effect on contact and retention.
When a fluid changes the jacket and seal differently, an isolated “compatible” result for either material leaves part of the interaction unexplored. I compare both materials under the same exposure, then examine the assembled pair. For example, a jacket that changes diameter during conditioning changes the seal’s compression as well. Check both the conditioned dimensions and the required sealing function using the specified test sequence.
Evaluate a replacement cable or sealing insert
I organize a replacement review around what has changed. Keep the approved gland configuration and installation method in view, then follow the changed material through to its contact and function.
- Identify the contact pair. Record the cable layer and compound, seal compound and part number. Keep the cable construction revision with them.
- Compare the fit. Measure the actual diameter range, ovality and surface features. Check these against the gland’s stated range and the layer the seal is intended to contact.
- Compare the duty. Use the entry temperature history, fluids, movement and duration to select relevant material data and conditioning.
- Assemble the specified combination. Follow the gland’s preparation, accessory and tightening instructions with the proposed cable or insert.
- Check the required functions. Apply the specified sealing, retention and inspection requirements after the relevant conditioning.
Consider a hypothetical cable replacement with the same nominal outside diameter but a different jacket compound. Its ovality, surface features and deformation under load may still differ. I use the selected gland and insert for both cables. Cable preparation and tightening stay consistent. Then I apply the same relevant conditioning sequence, such as a hot dwell followed by the plant’s cleaning cycle. Check the required seal and retention functions at the stages specified by the procedure. If the procedure includes inspection of the contact surfaces, look for jacket indentation, swelling, cracking or insert damage. Relate each finding to the functional results. Keep sample identity and actual dimensions with the comparison. Keeping the assembly method consistent makes material effects easier to identify. Use the results to decide which contact needs a different jacket or insert.
IEC 62444:2010 addresses construction and performance of complete cable glands as supplied. Keep the proposed cable and sealing option within the product’s intended configuration, and connect the replacement check to the assembled functions. When testing is required, retain the sample identities, installed condition, exposure sequence and results so the decision can be reproduced.
Conclusion
I compare cable jackets and gland seals as a contact pair. First identify the cable layer under each seal. Then use PE, XLPE, PUR, TPU or TPE to understand the material family and structure, and the compound and part identities to make the specific comparison.
The useful selection is the pair that fits and maintains its required function through the actual temperature, fluids, compression and movement. For a replacement, follow the changed material through those conditions and verify the resulting assembled contact.
FAQ
Does XLPE insulation mean the gland contacts XLPE?
An XLPE-insulated cable can have a different outer jacket. For an outer-sheath seal, identify that jacket from the construction drawing. If the gland seals bedding or another inner layer, identify that surface separately and use the relevant seal arrangement and preparation instructions.
Are PUR and TPU interchangeable names?
PUR identifies the polyurethane family. TPU identifies thermoplastic polyurethane within that family. I compare the actual compound, processing class and relevant test conditions when selecting an alternate jacket or seal, so that the broader PUR label is connected to a specific material.
Is every TPE a polyurethane?
TPE includes several thermoplastic-elastomer chemical systems. TPU is one member of that category. Identify the subtype, exact compound and molded-part geometry to compare fluid response, compression behavior and temperature performance for the seal being considered.
Can matching cable diameter and seal hardness approve a replacement?
Diameter and hardness help compare candidates. I also check the jacket compound, surface, ovality, seal geometry, installation and service history. Use the sealing and retention requirements for the assembled combination after the relevant conditioning to decide whether the replacement meets its duty.
Sources and technical references
- NIST — Thermal Exposure of Objects Near Burning Electrical Enclosures, TN 2320, Section 4, accessed 2026-10-28.
- IUPAC — Compendium of Polymer Terminology and Nomenclature, 2008 recommendations, accessed 2026-10-28.
- Javni et al. — Thermoplastic polyurethanes with controlled morphology, original research hosted by NIST, accessed 2026-10-28.
- SIS — ISO 16365-1:2025, thermoplastic polyurethane designations, accessed 2026-10-28.
- SIS — ISO 18064:2022, thermoplastic-elastomer nomenclature, accessed 2026-10-28.
- NIST — Viscoelastic Constitutive Model for the Creep Response of Polyurethane Rubber, accessed 2026-10-28.
- SIS — ISO 1817:2026, effect of liquids on vulcanized or thermoplastic rubber, accessed 2026-10-28.
- IEC — IEC 62444:2010, cable glands for electrical installations, accessed 2026-10-28.