Butyl Rubber (IIR) vs Nitrile Rubber (NBR): A Material Comparison

Butyl rubber (IIR) and nitrile rubber (NBR) are frequently placed side by side on a materials shortlist, and almost as frequently compared on the wrong axis. They are not two grades of the same thing. They are two polymers designed around two different problems, and the sensible way to choose between them is to identify which problem your joint actually has.

The difference starts at the molecule.

• Butyl rubber (IIR) is a copolymer of isobutylene with a very small amount of isoprene. The isobutylene units give the chain a dense, tightly packed methyl-group structure that severely restricts the diffusion of gas molecules through the bulk. The tiny isoprene fraction exists only to provide the few unsaturation sites needed for crosslinking. Because the backbone is almost entirely saturated, there is very little for ozone or oxygen to attack
• Nitrile rubber (NBR) is a copolymer of butadiene with acrylonitrile. The acrylonitrile content introduces polar nitrile groups along the chain. Non-polar hydrocarbon fluids — mineral oils, fuels, greases — do not swell a polar polymer well, which is precisely why NBR resists oil. Raise the acrylonitrile content and oil resistance improves; lower it and low-temperature flexibility improves

Everything else follows from those two facts. NBR's polarity buys oil resistance but leaves an unsaturated butadiene backbone that ozone and UV can attack. Butyl's saturated backbone buys outstanding weathering and gas tightness, but a non-polar hydrocarbon polymer sitting in mineral oil will swell.

1. Ask what the seal contacts. If the joint is wetted by fuel, mineral oil, hydraulic fluid, or grease, that constraint dominates and points toward NBR
2. Ask what the seal must keep out or in. If the requirement is to stop moisture vapour, air, or gas from crossing the joint over years, that points toward butyl
3. Ask where the joint lives. Exposed to weather, ozone, and sunlight, an unprotected NBR seal ages faster than a butyl one
4. Ask whether the joint moves. Dynamic sealing with reciprocating or rotating motion is O-ring and lip-seal territory. Butyl compounds serve static, permanently tacky sealing duties — a different application class altogether

Framed this way, the two materials rarely compete for the same part. They compete for the same shortlist because both are called "rubber."

Below is the practical comparison most procurement teams need. Garmy's figures are the published specifications of our butyl compound grades; the NBR column reflects the general characteristics of the material class, and any specific NBR grade should be confirmed with its own supplier because acrylonitrile content shifts NBR's behaviour substantially.

Property	Butyl Rubber (IIR)	Nitrile Rubber (NBR)	Which Wins
Oil & fuel resistance	Poor — swells in mineral oil, fuel, grease	Excellent — the defining property of the class	NBR
Gas & vapour impermeability	Outstanding — among the best of all elastomers	Moderate	Butyl
Weathering, ozone & UV resistance	Excellent — saturated backbone	Poor to fair — unsaturated backbone needs protection	Butyl
Water & moisture barrier	Excellent	Good	Butyl
Vibration damping (energy loss)	Excellent — high damping is intrinsic	Moderate	Butyl
Service temperature	-40°C to +120°C (Garmy butyl compound, published)	Typically around -30°C to +100°C depending on grade	Butyl (wider published span)
Abrasion & tear resistance	Moderate	Good	NBR
Permanent tack / self-adhesion	Excellent — non-curing butyl stays tacky indefinitely	Not a characteristic use	Butyl
Typical product form	Compound, tape, sheet, damping pad	Moulded O-rings, gaskets, hoses, seals	—

Three of these rows deserve elaboration:

• Gas impermeability is butyl's signature. The reason inner tubes and tyre inner liners are butyl is that its packed isobutylene structure makes gas diffusion extraordinarily slow. Translated into industrial sealing, this is what lets a butyl bead keep moisture out of a headlamp housing, an electrical enclosure, or an insulating glass unit for decades
• Oil resistance is NBR's signature — and butyl's weak point. No amount of compounding turns a non-polar hydrocarbon elastomer into an oil-resistant one. If your seal sits in engine oil or fuel, this is not a trade-off to negotiate; it is a disqualification
• Weathering runs the other way. NBR's butadiene backbone carries double bonds that ozone attacks, which is why exposed NBR parts crack over time unless protected by antiozonants or by design. Butyl's near-saturated backbone simply has far less to attack, and Garmy's compounds are rated to 120°C heat and -40°C cold across the HY-1, HY-2, CN-1, and CN-FR grades

The honest summary: NBR is the right elastomer for fluid-contact and dynamic sealing. Butyl is the right elastomer for static, long-life barrier sealing against water, air, and weather — and for damping.

If your requirement is a long-life moisture and gas barrier rather than oil contact, Garmy's butyl compound range is engineered for exactly that duty.

In practice, most sealing decisions resolve quickly once the duty is described precisely. Here is how the two materials divide the field across the segments Garmy supplies.

• Automotive body and lighting sealing → butyl. Headlamp and tail lamp sealing, door panel moisture barriers, sunroof perimeters, and trunk lid sealing are static joints whose job is to exclude water and vapour for the life of the vehicle. NBR brings nothing useful here; butyl's impermeability and permanent tack are decisive
• Engine bay fluid seals → NBR. Oil pan gaskets, fuel line seals, and hydraulic O-rings sit in exactly the fluids that swell butyl. Specify NBR (or a fluoroelastomer for higher temperatures) and do not attempt to substitute
• NVH and vibration damping → butyl. High intrinsic damping makes butyl the standard constrained-layer damping material for roof, fender, and floor panels. NBR is not a damping material of choice
• Building envelope and waterproofing → butyl. Window perimeter sealing, roofing joints, curtain wall joints, and below-grade waterproofing are weather-exposed, long-life, static duties. NBR's ozone sensitivity is a liability outdoors; butyl's saturated backbone is an asset
• Electrical and electronic enclosures → butyl. Cable joint insulation, enclosure sealing, PCB moisture barriers, and connector waterproofing all demand a vapour barrier rather than fluid resistance
• Dynamic seals with motion → NBR. Reciprocating rods, rotating shafts, and compression-set-critical O-rings are a moulded-goods application class that butyl sealing compounds do not address

A compact decision sequence for a new part:

1. Is the seal wetted by oil, fuel, or grease? If yes, stop — NBR or a fluoroelastomer. Butyl is out
2. Is the joint dynamic? If yes, you need a moulded dynamic seal, not a sealing compound
3. Is the primary requirement to block water, vapour, or gas over many years? If yes, butyl is the strongest candidate in the elastomer field
4. Is the joint weather-exposed or ozone-exposed? Butyl gains further advantage here
5. Does the application need damping as well as sealing? Butyl handles both in one material
6. Is there a fire requirement? Specify the flame-retardant CN-FR grade (UL94 V-0) rather than a standard compound
7. Confirm the temperature window. Garmy butyl compound is rated -40°C to +120°C; check that against your worst-case duty cycle

Where both materials could technically work — a static, dry, indoor gasket, for instance — the tiebreakers are usually installation method and cost. A self-adhesive butyl tape or compound needs no primer, no heat, and no fastener, which often removes an entire process step compared with a moulded gasket.

Not sure which side of the line your application falls on? Send us the fluid contact, temperature range, and substrate, and our technical team will tell you plainly whether butyl is the right material.

Q: Can butyl rubber be used in contact with oil or fuel?

A: No, and this is the clearest dividing line between the two materials. Butyl is a non-polar hydrocarbon elastomer, so mineral oils, fuels, and greases swell it. NBR resists those fluids because its acrylonitrile content makes the polymer polar. If your joint is wetted by oil or fuel, specify NBR or a fluoroelastomer — this is a disqualification for butyl, not a trade-off to be compounded around.

Q: Why is butyl so much better at blocking gas and moisture?

A: Butyl's chain is built almost entirely from isobutylene units, which pack densely and leave very little free volume for gas molecules to diffuse through. That structure gives butyl gas impermeability that is among the best of any elastomer, which is why it is used for tyre inner liners and why it excels as a long-life moisture barrier in headlamp housings, electrical enclosures, and building joints.

Q: Which has the wider service temperature range?

A: On published figures, butyl. Garmy's butyl compound is specified from -40°C to +120°C across the HY-1, HY-2, CN-1, and CN-FR grades, with the SD-1 and S-3 tape grades rated to 110°C. NBR's usable range varies with acrylonitrile content and is generally narrower, typically in the region of -30°C to +100°C, so confirm the exact figures with your NBR supplier for the specific grade.

Q: Does NBR weather better than butyl outdoors?

A: No — the opposite. NBR's butadiene backbone contains double bonds that ozone and UV attack, so exposed NBR parts tend to surface-crack over time unless protected. Butyl's near-saturated backbone gives it far better intrinsic ozone, oxidation, and weathering resistance, which is why butyl dominates outdoor and building envelope sealing.

Q: Can I replace an NBR gasket with butyl tape to simplify assembly?

A: Sometimes, and it is worth evaluating — but only if the joint is static and sees no oil, fuel, or grease. Where those conditions hold, a self-adhesive butyl tape or compound removes fastening and primer steps and provides a continuous, permanently tacky barrier. Where the joint is dynamic or fluid-wetted, the substitution will fail. Send us the duty conditions and we will advise honestly whether the swap is viable.

Q: Is Garmy a manufacturer or a distributor?

A: A manufacturer. Garmy has produced butyl compounds since 1999 at our own 4,200 m² plant in Eumseong, Chungbuk, Korea, with annual output of over 3,400 tonnes. We hold IATF 16949, ISO 9001, and ISO 14001 certification, three patents, and the Hyundai SQ mark, and we currently export to six countries. We do not produce NBR — if your application needs nitrile, we will tell you so directly.

Ready to confirm whether butyl is the right material for your seal?