What is a natural rubber?

Production lines fail when seals crack, mounts tear, or wheels slip. The wrong material is usually the reason. I see it every week.

Natural rubber is a polymer from Hevea tree latex (cis-1,4-polyisoprene). It offers very high elasticity, tear strength, and fatigue resistance, but it dislikes oils, fuels, ozone, and high heat.

I write this as a factory owner who molds rubber every day. I explain what natural rubber is, how we make it, when to use it, when not to use it, and how to spec it right.

How is natural rubber produced from latex?

Projects stall when material quality drifts. Moisture, dirt, or high ash in latex cause rejects.

Natural rubber comes from tapping Hevea brasiliensis. We collect latex, preserve or coagulate it, wash and sheet it, then dry and grade it (RSS, TSR/SMR, CV).

From tree to compound: what I control

I start at the cup. Workers tap the bark to let latex¹ drip into a cup. We stabilize fresh latex with small ammonia to stop premature coagulation. There are two main paths. One is field coagulation², where we add acid, then wash and mill the crumb into sheets. We smoke and dry these sheets to make RSS (Ribbed Smoked Sheet). The other is modern TSR/SMR³ (Technically/Standard Malaysian Rubber). We coagulate, shred, wash, dry, and bale rubber crumb under tighter process control. For stable viscosity in mixing, we use CV (Constant Viscosity⁴) grades.

Quality control starts early. I monitor dirt, ash, nitrogen (proteins), Mooney viscosity⁵, and PRI (Plasticity Retention Index⁶). Dirt raises wear in our mills. High ash reduces mechanical strength. I keep moisture low before shipping bales, since trapped water makes porosity in molded parts. Before compounding, I test Mooney to set mixing energy and time. I also screen for gel to avoid surface defects.

Common NR grades and uses

✅ I request TSR/SMR CV for consistent molding.
✅ I check PRI for oxidation resistance during processing.
🛠️ Tip: For tight tolerances and smooth skins, CV grades give fewer surprises.

What are the key properties of natural rubber⁷?

Soft seals feel nice, but strength and rebound do the real work.

Natural rubber combines high tensile strength, high elongation, excellent resilience, and low heat build-up. It handles cold well, but it struggles with oil, ozone, and heat above ~80 °C.

Why NR feels “alive” under load

The polymer chain in NR is mostly cis-1,4-polyisoprene⁸. This structure gives strong strain-induced crystallization. Under tension, NR forms micro-crystals that resist tear and cut growth. That is why it shines in dynamic parts. Its hysteresis⁹ is low, so it stays cool in flexing service. Its glass transition is low, so it keeps flexibility at low temperatures. The rebound is high, so it returns energy and damps noise in a pleasant way.

However, NR is unsaturated, so ozone cracks it outdoors if unprotected. Hydrocarbons and oils swell it. Heat above ~80 °C speeds aging and hardening. We can add wax, antioxidants, and antiozonants to slow this, but chemistry still rules.

Typical molded NR compound data (indicative)

✅ I pick 60–70 ShA for general mounts and wheels.
✅ I add wax bloom for outdoor parts that cannot be painted.
🛠️ Tip: If you need both resilience and moderate oil resistance, look at HNBR instead.

Where is natural rubber used in industry?

Wrong application wastes money. Right fit cuts vibration, noise, and downtime.

NR fits dynamic, non-oil environments: anti-vibration mounts¹², bushings, springs, rollers, non-marking wheels, conveyor lagging, and impact pads. It also works in water seals at moderate temperatures.

Use cases I recommend—and the limits I set

I use NR when I need high rebound and tear strength¹³. In plants, NR isolates compressors and fans with sandwich mounts. It carries loads in castor wheels without marking floors. It grips on conveyor drive rollers. It cushions impacts on bump stops and dock fenders. In water systems, NR gaskets seal at room temperature with low compression set¹⁴.

For HVAC, NR works in vibration isolators and hanger mounts. For mining, NR linings resist wet abrasion and impact. In food handling (dry), non-marking NR wheels move racks quietly. Yet I never use NR in oil sumps, diesel contact, or outdoor ozone without protection.

Application matrix

✅ I tune hardness to push the natural frequency below running speed.
✅ I finish-grind wheels for roundness and low runout.
🛠️ Tip: For outdoor parts, add UV-stable paint¹⁵ or a cover to block ozone.

What are the disadvantages of natural rubber?

Nice elasticity hides weak chemistry. Failures appear in weeks near oil, ozone, or heat.

NR has poor resistance to oils, fuels, and ozone. Heat aging is fast above ~80 °C. It is not ideal for chemicals. For these cases, use NBR, HNBR, EPDM, FKM, or silicone.

When I do not choose NR—and what I choose instead

I avoid NR near lubricants, fuels, or hydraulic oils. NBR or HNBR perform much better there. I avoid NR outdoors in sun and ozone unless I can shield it or use a protective coating; EPDM is far safer for weather and hot water. For high heat, silicone or FKM are the usual answers. For strong chemicals or solvents, FKM wins again.

Allergy is a topic for dipped latex goods, not solid molded NR, but I still note it for sensitive applications. For critical medical or food contact¹⁶, we often switch to platinum-cured silicone or to synthetic polyisoprene¹⁷.

Performance snapshot (typical)

Legend: ◎ excellent, ◯ good, △ fair, ✕ poor

✅ I explain trade-offs before tooling.
✅ I document compatibility to prevent field surprises.
🛠️ Tip: If you only need NR-like feel without oil issues, try synthetic polyisoprene¹⁷ (IR).

How do I choose a natural rubber grade for seals and parts?

A quick checklist avoids most mistakes. I keep it simple and strict.

Match environment, motion, and load. Set hardness for deflection. Confirm temperature, fluids, and ozone. Add protection or choose an alternative when risks appear.

My step-by-step selection playbook

I start with the environment. If oil, fuel, or solvent is present, I stop and switch to NBR/HNBR/FKM. If outdoor weather or hot water is involved, I prefer EPDM. If the environment is dry, clean, and at room temperature, NR is on the table.

Next, I classify the part. Static seals need compression set control. Dynamic parts need fatigue and tear strength. For mounts, I calculate natural frequency from load and target isolation. I pick hardness accordingly: 50–60 ShA for soft isolation, 60–70 ShA for general, 70–80 ShA for heavy loads. I define compression or deflection at work to stay within 10–25% strain for long life.

Then, I check certifications. For drinking water, I do not use NR; EPDM with WRAS/NSF options is safer. For food contact, I switch to FDA-grade silicone or EPDM, since proteins in NR complicate compliance.

Finally, I lock a specification. I state base polymer (NR), hardness, tensile and tear targets, compression set at service temperature, color, and tolerance class (ISO 3302-1). I include bonding system if metal inserts are used. I plan for wax/antiozonant or coating.

Quick decision table

✅ I include a simple sample plan to verify hardness, tensile, tear, and set.
✅ I run 10⁵–10⁶ cycle fatigue checks for mounts.
🛠️ Tip: If you need NR’s snap but better aging, consider NR/BR blends or NR with modern stabilizer packages.

Conclusion

Natural rubber excels in dynamic, clean, moderate-temperature work. I use it for mounts, wheels, and pads, and I avoid it near oil, ozone, or high heat.

Need help choosing NR or an alternative?
I can review drawings, materials, and tolerances, and suggest a risk-free plan.

• Website: www.rubberandseal.com
• Email: info@rubberandseal.com
• Brand: Julong Rubber, China — factory, wholesale only