A sensor cable may look simple from the outside, but the outer jacket has a difficult job.

It must protect conductors, sensor wires, shielding layers and internal reinforcement from moisture, abrasion, temperature changes, chemicals and mechanical stress. In grain storage applications, the challenge becomes even greater because the cable may remain buried inside wheat, corn, soybeans or other bulk materials for years while the grain moves, settles and rubs against its surface.

Choosing the correct jacket material can significantly extend cable life. Choosing the wrong one can lead to cracking, water ingress, damaged conductors and unstable sensor readings long before the sensing element itself reaches the end of its service life.

What Does a Sensor Cable Outer Jacket Actually Do?

The jacket is the cable's outer protective layer. It does not normally carry the electrical signal, yet it directly affects how well the cable survives in the field.

A good jacket protects the internal cable structure against several types of stress at the same time:

• abrasion and repeated contact
• moisture and condensation
• oils and chemicals
• sunlight and outdoor exposure
• low and high temperatures
• bending and flexing
• mechanical impact
• dust and contamination

For a stationary indoor sensor cable, these requirements may be relatively modest.

A temperature cable hanging inside a 20-meter or 30-meter grain silo faces a completely different environment. Grain is loaded, stored and discharged. The cable remains inside that moving mass, where it experiences friction, pressure and tensile forces over and over again.

That is why cable jacket selection should begin with the application, not with the material name.

Common Sensor Cable Jacket Materials

Several materials are widely used for industrial sensor and instrumentation cables. Each one has strengths, limitations and an ideal working environment.

There is no single "best" jacket.

A jacket that performs exceptionally well on a robotic machine may be unnecessarily expensive for a stationary grain temperature cable. A rigid material that works well in a silo may be uncomfortable to handle on a portable measuring instrument.

The environment decides.

HDPE: A Strong Choice for Fixed Grain Monitoring Cables

High-density polyethylene, or HDPE, is particularly attractive when moisture resistance and mechanical protection matter more than extreme flexibility.

It has low water absorption and good resistance to many environmental contaminants. Its relatively hard surface also makes it suitable for cables that remain in contact with bulk materials for long periods.

For a grain temperature cable suspended vertically inside a silo, that combination is useful.

The cable may spend years surrounded by grain. Every filling and discharge cycle creates movement around the cable, and the jacket must protect the electrical core from that repeated mechanical contact.

HDPE also works well for outdoor sections of industrial cables when the correct UV-stabilized formulation is selected.

For many stationary grain-storage applications, it offers an effective balance between:

durability + moisture protection + cost + mechanical strength.

LLDPE: Similar Protection, More Flexibility

Linear low-density polyethylene, usually called LLDPE, belongs to the same broad polyethylene family but feels noticeably different in practical cable construction.

It is generally softer and more flexible than HDPE.

That matters when the cable has a relatively large diameter or must be coiled during shipping and installation. A very rigid cable can be difficult to handle, particularly when installers are working on silo roofs or routing long sections through support structures.

LLDPE still provides strong resistance to water and environmental exposure while making the finished cable easier to bend.

For this reason, LLDPE is often worth considering for:

• multi-point temperature cables
• temperature and humidity sensor cables
• large-diameter armored sensing cables
• long cable assemblies that must be coiled for transport
• applications requiring moderate flexibility without moving to an expensive PUR construction

HDPE and LLDPE should therefore be viewed as different tools rather than competing materials.

HDPE favors rigidity and mechanical protection.
LLDPE favors toughness with improved flexibility.

PVC: Practical and Economical

PVC remains one of the most widely used cable jacket materials because it is affordable, versatile and easy to process.

Modern PVC formulations can provide good abrasion resistance and reasonable resistance to moisture, making them suitable for many ordinary industrial applications. igus, for example, uses PVC in flexible industrial cable families and notes its attractive price-to-performance ratio for appropriate applications. 

PVC makes sense for:

• indoor sensor wiring
• control cabinets
• short instrumentation cables
• equipment with limited cable movement
• cost-sensitive projects

Its limitations become more noticeable in harsher environments.

Very low temperatures, intensive outdoor exposure, strong chemicals or high-frequency flexing may justify moving to another material.

That does not make PVC a poor material. It simply means that the formulation and application need to match.

PVC, PUR and TPE Cable Jacket Materials – igus

PUR and TPU: When the Cable Has to Move

A fixed cable and a moving cable experience very different types of stress.

If a cable is repeatedly dragged across a machine, bent around rollers, routed through a cable carrier or twisted by robotic equipment, flexibility becomes just as important as environmental protection.

This is where PUR, or polyurethane, performs particularly well.

PUR jackets are widely used in demanding motion applications because they can offer strong abrasion, notch and cut resistance while remaining flexible. Industrial PUR cables are also commonly designed for oily or chemically demanding environments. 

For example, LAPP describes PUR-jacketed industrial cables designed to withstand mechanical stress, abrasion, notches and cuts, including continuously flexing applications. 

PUR or TPU is therefore a good candidate for:

• portable sensor probes
• mobile temperature measurement equipment
• drag-chain cables
• robotic systems
• cables that are repeatedly wound and unwound
• equipment exposed to abrasion and movement

For a permanently suspended grain-silo cable, however, that level of dynamic flexibility may not be necessary. HDPE or LLDPE can often provide a more economical solution.

LAPP PUR Cable Example

TPE: Built for Flexibility and Repeated Motion

Thermoplastic elastomers, or TPEs, combine some characteristics of rubber with thermoplastic processing.

The material is particularly useful where repeated bending, tight bending radii or high-speed movement are expected. igus describes TPE cable compounds as suitable for substantial mechanical loads as well as exposure to chemicals and temperature extremes in appropriate cable designs. igus

TPE is often selected for sophisticated moving equipment rather than simple stationary sensor installations.

The material can be excellent.

The question is whether the application really needs it.

High Temperatures and Aggressive Chemicals Need a Different Strategy

Standard PE and PVC cables cover a huge range of industrial applications, but there are environments where conventional materials stop being practical.

Imagine a sensor cable installed close to hot processing equipment, inside a chemical plant or in a system exposed to solvents, fuels and acids.

The jacket now has to survive much more than moisture and abrasion.

Materials such as FEP and PTFE become attractive.

Alpha Wire, for example, specifies FEP-jacketed industrial cable designed for extreme chemical exposure and a temperature range extending from approximately -80°C to +200°C in its Xtra-Guard 5 family. 

This level of performance comes at a price, so fluoropolymer jackets normally make sense when the environment actually demands them.

Alpha Wire Xtra-Guard 5 FEP Cable

Grain looks soft when held in your hand. Inside a large silo, it behaves very differently.

Thousands of tons of material produce substantial pressure. When grain enters or leaves the silo, particles move vertically and laterally around the temperature cables.

That movement creates friction.

The cable also needs to tolerate dust, humidity and possible condensation while continuing to provide reliable temperature measurements over many storage cycles.

Grain temperature monitoring systems therefore use vertically suspended sensor cables at multiple positions throughout the stored material so operators can identify developing temperature differences or hotspots. Real-world commercial systems use this same distributed-cable concept.

A suitable jacket does not improve temperature accuracy directly, but it protects the physical infrastructure that allows accurate measurements to continue year after year.