IRHD hardness (International Rubber Hardness Degree / ball indentation hardness)

What is IRHD hardness testing?

The IRHD (International Rubber Hardness Degree) hardness test is a standardised method for determining the hardness of elastomers. It is based on the ball indentation method, in which a defined ball penetrates the material with a defined force. The method is particularly suitable for small, thin or sensitive samples and offers reproducible, comparable results.

How does the IRHD measurement work?

The test is carried out in accordance with DIN ISO 48-4, whereby a ball with a defined geometry and force is pressed vertically onto the material. Depending on the penetration depth, a hardness value is obtained on a scale from 0 (soft) to 100 (hard). There are different scales, which are selected depending on the specimen:

IRHD-M: Microhardness
IRHD-L: Low hardness
IRHD-N: Normal hardness
IRHD-H: High hardness

These 4 scales are also available in a modified form for round specimens. The diameter of the test ball and the force applied differ depending on the scale.

Comparison of IRHD hardness test and Shore hardness test:

Criterion	IRHD hardness test	Shore hardness test
Range of materials	Elastomers	Elastomers and plastics
Test specimen	Hemisphere	Truncated cone
Precision	Very good	Good
Test procedure	Non-destructive	Destructive (leaves an imprint)

Although both methods measure hardness on a scale of 0 to 100, the hardness values cannot be converted directly into each other.

Further entries

RTV silicone: Room temperature curing solid silicone

RTV silicone is a room temperature curing silicone rubber that cures without heat or pressure. It is particularly suitable for sealing, bonding, potting and mould making and is less strong and temperature-resistant than HTV and LSR.

Rubber buffers

Rubber buffers are elastic elements that absorb and dampen shocks, oscillations and vibrations. They protect machines, devices and assemblies from mechanical loads, compensate for movements and reduce noise in technical applications.

Sealed seats

Sealing seats are machined contact surfaces that accommodate seals in a form-fit and force-fit manner, thus ensuring permanent media separation protection.

Series production

Series production refers to the repeated, economical manufacture of similar components in large quantities.

Shaft seal

A shaft seal is a sealing element that seals between a rotating shaft and a housing. It prevents lubricants from escaping and at the same time protects against dirt, dust and moisture.

Elongation at break

The elongation at break indicates how much a material can stretch under tensile load before it tears.

PC: Polycarbonate

Polycarbonate (PC) is a transparent, impact-resistant plastic that is used for high-quality housings, visible parts and functional composite components.

LSR: Liquid silicone

LSR is a liquid silicone rubber produced on a VMQ or FVMQ basis and processed by injection moulding. The material combines high elasticity, purity and temperature resistance.

PPS: Polyphenylene sulphide

Polyphenylene sulphide (PPS) is a high-temperature and chemical-resistant precision plastic that is used in media-exposed and dimensionally critical components, especially in hybrid solutions.

Rubber-Plastic Composite Parts

Rubber-plastic composite parts are hybrid components in which elastic and thermoplastic components are functionally combined - ideal for seals, housings and flexible technical solutions.

Deburring

Deburring is the process of removing burrs from components to ensure the function, appearance and safety of technical products.

Primer

Primers are adhesion-promoting primers that improve the adhesion between rubber, plastic or metal and ensure a permanent bond in composite and coating applications.

PU: Polyurethane elastomer

PU elastomers are dimensionally stable, abrasion-resistant plastics with high mechanical strength that are ideal for rollers, seals and shock absorbers in heavy-duty industrial applications.

Metal oxide crosslinking

Metal oxide crosslinking is a crosslinking process that is mainly used for chloroprene rubber and produces particularly durable, ageing and flame-resistant rubber parts.

TPE: Thermoplastic elastomers

TPEs are elastic, malleable materials with rubber-like behaviour that can be thermally processed and recycled like plastics - ideal for flexible seals, handles and hybrid parts.

IIR: Butyl rubber

Butyl rubber (IIR) is a particularly gas-tight, weather- and chemical-resistant elastomer that is mainly used in tyres, seals and membranes.

Extrusion of rubber

Rubber extrusion is a continuous manufacturing process for rubber-elastic profiles, hoses and seals in which the material is pressed through a moulding die and then vulcanised.

Compression moulding

Compression moulding is a process for manufacturing moulded rubber parts in which a rubber compound is compressed under pressure and heat in a closed mould and vulcanised directly.

Rubber blank

A rubber blank is a non-crosslinked, mouldable elastomer precursor that is processed in moulding tools to produce elastic rubber parts.

Cycle time

The cycle time describes the complete duration of a production run during injection moulding or pressing and is a key parameter for efficiency and output.

IRHD hardness (International Rubber Hardness Degree / ball indentation hardness)

IRHD hardness is an internationally standardised method for measuring rubber hardness using ball pressure and is particularly suitable for small or sensitive elastomer components.

Copolymerisation

Copolymerisation is the simultaneous polymerisation of different monomers to produce polymers with specifically adjustable properties for technical and industrial applications.

DIN ISO 3302-1

DIN ISO 3302-1 defines the general tolerances for moulded rubber parts and is an international standard for ensuring dimensional accuracy in elastomer processing.

Saturated and unsaturated polymers

Saturated polymers have only single bonds in the main chain and are resistant to ageing, while unsaturated polymers contain double bonds in the main chain and are easier to crosslink; EPDM is a speciality because its double bond is in the side chain.

Sulphur crosslinking

Sulphur crosslinking is a proven vulcanisation process in which rubber is crosslinked with the aid of sulphur to form an elastic, dimensionally stable and mechanically resilient material.

LABS (paint wetting impairment substances)

LABS are substances that interfere with the wetting of paints and must therefore be strictly avoided or tested in paint-critical applications.

Rapid tooling

Rapid tooling is the accelerated production of functional tools for the rapid production of prototypes or small series under near-series conditions.

Oil resistance

Oil-resistant materials permanently withstand aggressive oils and are used in seals, hoses and technical components.

Fillers

Fillers are functional additives in rubber or plastic compounds that specifically influence mechanical properties, processability or cost structure.

Caoutchouc vs. rubber vs. elastomer

Rubber is the raw material, rubber is the end product created by vulcanisation, and elastomer is the superordinate material class of elastic polymers.

SBR: styrene-butadiene rubber

SBR is a cost-effective, abrasion-resistant elastomer with good mechanical properties that is mainly used in tyres, seals and general moulded rubber parts.

Glass transition temperature

The glass transition temperature (Tg) is the temperature range in which a polymer changes from elastic to glassy and largely determines its low-temperature flexibility.

brass

Brass is an easily machinable, corrosion-resistant copper-zinc alloy that is widely used as a functional and decorative metal - including in rubber-metal composite parts, fittings and electrical components.

GRP: Glass fibre reinforced plastic

GRP (glass fibre reinforced plastic) is a robust, lightweight composite material made from glass fibres and a plastic matrix that is used in a wide range of applications in industry, construction and mobility.

ISO 9001

ISO 9001 is the world's most important standard for quality management. It defines how companies manage their processes so that products and services deliver consistently high quality and fulfil customer requirements.

Silane crosslinking

Silane crosslinking is a moisture-controlled crosslinking process for plastics and elastomers that enables mechanical stability at moderate processing temperatures.

Synthetic rubber

Synthetic rubber is an industrially manufactured elastomer material that is categorised into main chemical groups and whose properties can be specifically adapted to technical requirements.

Tool cleaning

Tool cleaning ensures reliable, clean moulding, protects against burr formation and extends the service life of tools in series production.

Titanium

Titanium is an extremely corrosion-resistant, lightweight and high-strength material that is used in aviation, medical technology and for rubber-metal composite parts in aggressive environments.

Compound

A compound is a customised material mixture of polymer and additives that is specifically tailored to the requirements of a particular technical application.

Suction pad

Suction cups are cup-shaped suction cups made of elastomer or plastic that cling elastically to the surface and trap the resulting vacuum. Suction cups create an adhesive connection between the gripper and the workpiece by means of negative pressure.

Calendering

Calendering is a rolling process in which rubber or plastic compounds are rolled between heated rollers. In addition to the manufacture of finished products such as rubber mats, it is primarily used in the production of rubber blanks.

Profile seal

A profile seal is a seal with a defined cross-sectional shape (round, rectangular, hollow or with a complex profile) that ensures a seal between two components. It is made from elastomers and is used wherever gaps, movements or unevenness need to be compensated for.

Autoclaves

An autoclave is a heatable pressure vessel for the thermal treatment of materials - e.g. for the post-vulcanisation of elastomers or for sterilisation in medicine and technology.

CAD modelling

CAD modelling is the digital design of technical components and tools that serves as the basis for production, simulation and prototype development in industry.

Stress cracking

Stress cracking is the gradual formation of cracks in plastics due to the interaction of stress and chemical media - often with critical consequences for component safety.

Shore hardness

The Shore hardness measures how deeply a test pin penetrates a material and thus provides information about its degree of hardness - a decisive factor in the selection of elastic and technical materials.

CR: Chloroprene rubber

Chloroprene rubber (CR) is a versatile, weather- and flame-resistant elastomer that is often used for seals, hoses and technical components for indoor and outdoor use and is also known as neoprene.

Vulcanisation

Vulcanisation is the process in which raw rubber is converted into a permanently elastic, dimensionally stable and durable rubber state through chemical cross-linking.

EPDM: Ethylene propylene diene rubber

EPDM is a weather, UV and chemical-resistant elastomer with high thermal stability that is used in particular for durable seals, hoses and outdoor applications in industry and construction.

Burr formation

Burr formation occurs in primary forming processes due to material escaping from mould parting surfaces and joints during forming and requires targeted reworking to ensure component quality.

Rubber

Rubber is an elastic material of natural or synthetic origin that is vulcanised into durable components for sealing, damping and technical applications.

Sampling

In engineering, sampling is the testing and approval of sample parts of a new or revised product or manufacturing process.

Heat resistance

Heat-resistant materials retain their properties at high temperatures and are ideal for industrial and technical applications.

Tensile strength

The tensile strength is the maximum stress that a material can withstand under tensile load and is a key parameter for the mechanical strength of elastomers.

ISO 13485

ISO 13485 explained: an overview of the requirements, areas of application and benefits of certification for medical technology.

Bellows

A bellows is an elastic component with a corrugated, accordion-like geometry that absorbs movements, changes in length or swivelling movements without losing its protective or sealing function. It protects sensitive components such as joints, shafts or guides from dirt and moisture and at the same time enables a flexible, permanently movable connection.

Rubber caps

Rubber caps reliably protect components from dust, moisture and mechanical impact.

Valves

Valves control, throttle or shut off liquids and gases in pipework, motors and hydraulic systems. They are crucial for process reliability and efficiency.

Plasticiser

Plasticisers are additives that make rubber and plastics more elastic and easier to process and are mainly used in flexible sealing and moulded parts.

Elasticity

Elasticity is the ability of a material to deform under load and then return completely to its original shape - essential for flexible technical components.

ABS: Acrylonitrile butadiene styrene

Acrylonitrile butadiene styrene (ABS) is a robust, impact-resistant and easy-to-process plastic that is used for housings, interior parts and rubber-plastic composite components with high surface and dimensional stability requirements.

EN 9100

EN 9100 explained: an overview of the requirements, areas of application and benefits of certification for the aviation, aerospace and defence industries.

Seals

Seals prevent leaks in pipework, motor and system components. They also compensate for manufacturing tolerances and protect processes against pressure, temperature and media stress.

Pressure resistance

Pressure resistance is the resistance of a material to compressive stress and is a decisive factor for the function and service life of technical components under mechanical stress.

PES: Polyester

Polyester (PES) is a robust, chemical-resistant thermoplastic that is used both as an engineering plastic and as a fabric reinforcement in rubber composite parts.

Express Services

Express production refers to the particularly fast production of prototypes, tools or small batches and accelerated development projects with drastically reduced delivery times.

Rubber-fabric composite parts

Rubber-fabric composite parts are elastic components with integrated fabric inserts that ensure high tensile strength, dimensional stability and dynamic load-bearing capacity - for example in membranes, seals or conveyor belts.

Anti-ageing agent

Anti-ageing agents are functional additives that protect elastomers and plastics from damaging influences such as oxygen, ozone, UV radiation or heat, thereby significantly extending their service life.

Prototype construction

Prototyping is the targeted production of functional sample parts for early testing and optimisation of geometry, material behaviour and processability before the start of series production.

Grommets

Grommets are ring- or disc-shaped protective inserts that are inserted into openings or edges to allow cables to pass through safely. Grommets protect cables and hoses from sharp edges, seal feed-throughs and can be quickly inserted into holes or gaps.

Sealing lips

Sealing lips are flexible sealing elements that securely enclose media and remain reliably functional even in the event of rotation or pressure fluctuations.

Aluminium

Aluminium is a lightweight, corrosion-resistant material with high thermal conductivity that is used in a variety of ways as a construction material and support element in technical components.

Rubber recycling

Rubber recycling includes mechanical, thermal and chemical processes for the reuse of vulcanised rubber products as raw materials or additives in new applications.

Adhesion

Adhesion is the physical holding force between two different materials at their interface and is a key factor for strong, durable connections in technology and industry.

Polymerisation

Polymerisation is the chemical reaction in which many monomers are combined to form long polymer chains - the basis for plastics and rubber elastomers.

Mould cavity / cavity

Mould cavities are the cavities in a mould that give the component its final geometry during the moulding process.

Adhesion promoter

Adhesion promoters are chemical bonding agents that permanently bond rubber with other materials and thus form the basis for resilient rubber composite parts.

Inserts

Inserts are solid components that are embedded in rubber components during processing in order to specifically extend their functionality, stability or fastening options.

CFRP: Carbon fibre reinforced plastic

CFRP (carbon fibre reinforced plastic) is an ultra-light, extremely strong composite material made of carbon fibres and a plastic matrix that is used in highly stressed lightweight construction applications.

PA: Polyamide

Polyamide (PA) is a robust, wear-resistant plastic with very good strength and chemical resistance, which is used in particular in technical components and rubber-plastic composite systems.

Peroxide crosslinking

Peroxides are reactive cross-linking chemicals that produce stable, temperature- and chemical-resistant elastomer structures without sulphur bridges in rubber processing.

HTV silicone: High-temperature curing solid silicone

HTV silicone is a high-temperature curing solid silicone rubber that becomes a permanently elastic material when heated. It combines high mechanical strength with excellent resistance to temperature, ageing and chemicals.

RoHS

RoHS restricts the use of certain hazardous substances in electrical and electronic equipment in order to reduce environmental and health risks. Products may only be sold in the EU if all components comply with the specified limits for listed hazardous substances.

Injection moulding

Injection moulding is a precise moulding process for manufacturing complex plastic and rubber parts in which the material is injected into a mould under pressure and cured there.

Assembly Services

Component assembly comprises the assembly of individual components into a functional unit as an assembly.

Tool costs

Tool costs are the expenses for the manufacture of tools and have a significant influence on the profitability of series production.

Housing and cover with integrated seal

Housings and covers with integrated seals are components in which the sealing function is embedded directly in the plastic or metal part. The sealing function is usually realised as an overmoulded or pressed-in rubber sealing lip. They enable reliable sealing without a separate sealing component and are often used for compact, easy-to-install assemblies.

Aramid / Kevlar

Aramid / Kevlar is an extremely tensile, lightweight and heat-resistant fibre that is used as reinforcement in rubber composite parts, sealing systems and protective applications.

Engine damper

Engine dampers are elastic elements that absorb vibrations and shocks between the engine and the vehicle or machine frame. They reduce vibrations, protect adjacent components from stress and improve the noise and running behaviour of the entire system.

Biocompatibility

The proof of biocompatibility proves through standardised tests that a medical device or material does not cause any harmful reactions in the human body.

Abrasion

Abrasion is the mechanically induced surface wear of a material caused by friction and has a decisive influence on the service life and usability of technical components.

Fatigue

Fatigue refers to the progressive degradation of material due to repeated mechanical stress and is a key factor in the design of durable technical components.

ISO 14001

ISO 14001 explained: an overview of the requirements, areas of application and benefits of the international standard for environmental management systems.

Residual materials

Residual materials are recyclable material residues from production that can be specifically collected and fed back into the production cycle to conserve resources.

Vibratory finishing (barrel finishing)

Mass finishing or barrel finishing is a mechanical mass finishing process in which surfaces are machined and burrs removed using abrasive media and movement.

Tempering

Annealing is a thermal post-treatment that reduces residual stresses, stabilises material properties and improves the functionality of technical components.

Toolmaking

In elastomer production, toolmaking refers to the development and manufacture of high-precision tools that are used in the production of rubber, plastic and composite parts for moulding.

VMQ: Silicone rubber

Silicone rubber (VMQ) is a heat-, cold- and UV-resistant elastomer with very good insulation and media resistance, which is frequently used in medical, food and automotive technology.

Protective housing

A protective housing encapsulates sensitive components and prevents damage caused by dirt, water or impact.

Elongation

Elongation refers to the change in length of a material under tensile load and is a key parameter for assessing the elasticity and breaking strength of technical materials.

Special alloys

Speciality alloys are highly developed metal mixtures for extreme requirements in technology, medicine and industry - especially where corrosion, temperature or load limits of standard materials are exceeded.

Azo and urea compounds

Azo and urea compounds are speciality chemicals that are used as blowing or cross-linking agents in rubber processing - especially for foams and friction-active components.

Medical device regulation (MDR)

The Medical Device Regulation (MDR) is the central EU regulation for medical devices, which places high demands on safety, documentation and market surveillance.

Cold resistance

Cold resistance describes the ability of a material to remain functional and elastic at low temperatures - crucial for seals and elastomer components in outdoor or cold applications.

Outgassing

Outgassing is the escape of volatile substances from materials and can lead to malfunctions, contamination or optical faults in sensitive applications.

Rubber expansion joints

Rubber expansion joints are flexible connecting elements that compensate for movements, vibrations and pressure surges in pipework. Thanks to their elastic structure, they can absorb changes in length, lateral displacements and angular movements and thus protect connected system components from mechanical stress, vibrations and tension in the pipework system.

Polyurethane (PU)

Polyurethane (PU) is a robust, abrasion-resistant plastic with high elasticity and chemical resistance, which is primarily used in heavily loaded technical components, dampers and composite solutions.

NBR: Acrylonitrile butadiene rubber

Acrylonitrile butadiene rubber (NBR) is an oil and fuel-resistant elastomer that is frequently used for seals, hoses and technical moulded parts in mechanical engineering and vehicle construction.

Rebound resilience

Rebound resilience describes the ability of a material to return energy after rapid deformation - crucial for dynamic applications such as spring elements or dampers.

Freeze deburring

Freeze deburring is a process for removing burrs, particularly on rubber parts, by cooling and mechanical blasting.

Degreasing

Degreasing is an essential cleaning step for removing residues from components to ensure optimum adhesion during vulcanisation, bonding or coating.

FKM: Fluororubber

FKM is a heat- and chemical-resistant high-performance elastomer for seals and components in extremely demanding industrial applications.

PP: Polypropylene

Polypropylene (PP) is a lightweight, chemical-resistant thermoplastic with a wide range of applications that is ideal for technical plastic parts and rubber-plastic composite solutions.

Crosslinking chemicals

Cross-linking chemicals ensure the permanent elasticity and dimensional stability of rubber through chemical reaction - a key component in the production of functional rubber parts.

Ageing

Ageing describes the gradual change in material properties due to external influences such as heat, UV radiation or media, which can lead to long-term impairment of function and service life.

FDA conformity

FDA compliance means that a material or product meets the requirements of the U.S. Food and Drug Administration and is safe for contact with food, drinking water or pharmaceutical applications. Only approved ingredients may be used and the material must not release any substances of concern into the medium.

FVMQ: Fluorosilicone

FVMQ is a cold-flexible, fuel- and weather-resistant fluorosilicone elastomer that is primarily used in the aviation and automotive industries for demanding sealing applications.

Elastomer rollers

Rubber rollers transmit forces, dampen vibrations and protect surfaces in printing machines, conveyor systems and packaging lines.

Keyboard and switch covers

Keyboard and switch covers are elastic protective components that protect keys and operating elements from dust, moisture and dirt. At the same time, they maintain the operating function by transmitting the actuation feel and enabling reliable sealing.

Molded Rubber Parts

Moulded rubber parts are elastic components made from vulcanised rubber by pressing, transfer moulding or injection moulding. They are manufactured according to drawings and are used as sealing, damping or functional elements in technical applications.

HNBR: Hydrogenated NBR

HNBR is a particularly heat-, oil- and ageing-resistant elastomer that is ideal for durable seals and technical components in dynamically stressed applications.

REACH

REACH is an EU regulation for the registration, evaluation and regulation of chemical substances in order to better protect people and the environment. Companies must prove the safety of the raw materials they use and inform customers if their products contain substances of concern.

Vibration dampers

Vibration dampers reduce vibrations and noise in machines and vehicles.

Vacuum cups

Suction cups are suction cups made of elastomer or plastic that cling elastically to the surface and trap the resulting vacuum. Suction cups create an adhesive connection between the gripper and the workpiece by means of negative pressure.

PPA: Polyphthalamide

Polyphthalamide (PPA) is a dimensionally stable, chemical and temperature-resistant high-performance plastic that is used in particular for precise, media-resistant components and rubber-plastic composite solutions.

Transfer moulding

Transfer moulding is a rubber moulding process in which the material is pressed from a heated chamber into a closed mould where it is cross-linked under pressure and temperature - ideal for precise components with inserts.

Valve seal

A valve seal is an elastic component that reliably seals the flow of gases or liquids in a valve. The seal prevents leaks, compensates for pressure and temperature changes and ensures that the valve fulfils its switching, control or shut-off function reliably and permanently.