How Rubber Track Compounds Are Made: NBR vs Natural Rubber Explained 

Most people buying a rubber track never think much about what it’s actually made of. They look at the price, check the dimensions, and get on with it. That’s understandable, but the compound is the track. It determines how the rubber holds up against sharp aggregate in WA, how it ages in the heat of a Darwin summer, and whether it survives in contact with the hydraulic fluid that inevitably ends up on a construction site. If you’re specifying tracks for a machine you rely on, it’s worth understanding the difference between natural rubber, NBR, and the blended compounds that make up most premium tracks today. 

What Goes into a Rubber Compound 

A rubber track compound isn’t a single material it’s a formulated mixture. The base polymer provides the elastic behaviour. Carbon black is added in substantial quantities to reinforce the matrix, giving it tensile strength and abrasion resistance that raw rubber couldn’t achieve alone. Plasticisers keep the compound pliable in cold weather. Antioxidants slow the hardening that comes from prolonged heat exposure. Vulcanising agents typically sulphur-based systems cross-link the polymer chains during the curing process to lock in the compound’s final properties. 

All of this is mixed in large internal mixers, calendered into sheets, laid up over the reinforcement cord, and then cured under heat and pressure in a mould. The exact ratios and grades of each ingredient determine the finished compound’s hardness, elasticity, cut resistance, and durability. This is where the real difference between a quality track and a cheap import lies not in what the track looks like, but in what it’s made of. 

Natural Rubber 

Natural rubber NR is tapped from Hevea brasiliensis trees and has been used in industrial rubber products for well over a century. Its appeal hasn’t faded: NR has a molecular structure that gives it tensile strength exceeding 20 MPa, outstanding elongation at break, and flex fatigue resistance that synthetic alternatives struggle to match. When a track bends around a drive sprocket hundreds of thousands of times over its working life, that resistance to flex fatigue is important. 

NR also bonds extremely well to brass-plated steel cord which matters enormously for track longevity, since delamination between the compound and the cord body is one of the primary failure modes in a worn track. 

The problem for Australian operators is heat. In the Pilbara, far north Queensland, and the NT, summer ground temperatures under steel plate can exceed 70°C. Natural rubber ages poorly under sustained heat it oxidises, hardens, and eventually cracks. NR also has limited resistance to oils and fuels, which means tracks on construction sites and in agricultural settings face ongoing chemical exposure the compound wasn’t optimised for. 

Nitrile Butadiene Rubber (NBR) 

NBR sometimes called Buna-N is a synthetic polymer made by co-polymerising butadiene and acrylonitrile. By adjusting the proportion of acrylonitrile (typically between 18% and 50%), the compounder can tune the material’s properties. Higher acrylonitrile content increases oil and fuel resistance; lower acrylonitrile content preserves more of the natural rubber-like flexibility. 

For construction sites and demolition applications, NBR’s advantages are meaningful. It doesn’t swell or soften when soaked in hydrocarbon fuels or hydraulic fluids. It can be formulated to higher hardness levels of Shore A 65 to 80 which resists cutting on concrete rubble and sharp aggregate. And it holds its hardness better than NR under sustained elevated temperatures. 

The trade-off is flex fatigue. An NBR compound that’s been pushed to Shore A 78 for hardness isn’t going to flex as gracefully as a soft NR compound. In agricultural applications machines work soft paddock ground with relatively small sprockets that can translate to earlier lug cracking. For most construction and urban work, the trade-off is worth making. 

TFI Technician Note: On Australian construction sites, we’re regularly dealing with a combination of concrete rubble, summer heat, and incidental oil contamination three things that challenge a pure natural rubber compound. Our ISO-certified NBR-blend formulation targets a Shore A hardness of 72 to 75. That’s firm enough to resist cutting demolition sites but still supple enough to pass our flex fatigue test to 500,000 cycles. 

Blended Compounds 

Most premium tracks today aren’t pure NR or pure NBR; they’re blended formulations designed to hit a specific combination of properties. Natural rubber provides the backbone: tensile strength and flex fatigue resistance. Synthetic polymers are added to address its weaknesses. 

SBR (styrene-butadiene rubber) adds abrasion resistance at lower cost and is commonly used in general-purpose blends. EPDM (ethylene propylene diene monomer) improves ozone and UV resistance dramatically relevant in Australia, where UV exposure is among the highest in the world and tracks on machines left outside age faster than they would in northern Europe. BR (polybutadiene rubber) improves low-temperature performance and flex fatigue without requiring a reduction in compound hardness. 

A well-engineered blend can target specific test thresholds: tensile strength above 18 MPa, elongation at break above 400%, Shore A hardness of 70 ± 5, and heat ageing resistance such that hardness changes after 72 hours at 100°C stays below 15%. These aren’t marketing numbers they’re compound specifications that a supplier should be able to back up with test certificates. 

What ISO Certification Actually Means 

Any supplier can claim their compound is premium. ISO certification means an independent auditor has verified that the formulation and manufacturing processes are documented, controlled, and consistent. When you buy a track from an ISO-certified facility, the compound in that track has been manufactured to a defined specification with the same specification as the previous batch and the next one. 

The relevant test standards are ISO 37 for tensile strength, ISO 48-2 for hardness, and ISO 188 for heat ageing resistance. When evaluating a track supplier, ask for their compound test certificates. If they can’t produce them, there’s no independent basis for any performance claim they’re making. 

Tradefaire International’s tracks are manufactured in ISO-certified facilities with consistent batch-to-batch compound control. That consistency matters if you’re running a fleet the track you order today will perform identically to the one you ordered last year. 

Choosing by Application 

If you’re not sure which compound specification suits your machine and operating environment, talk to our technical team before ordering. Specifying the right compound upfront is considerably cheaper than replacing tracks prematurely. 

Call 1300 916 556 or visit tradefaire.com.au to discuss your application.