Glossary & FAQs

Answers to all of your silicone rubber related questions, written by our industry experts.

A diagram of a square-angled U-shape rubber extrusion, with dimensions for each side.

Silicone rubber is an elastomer composed of silicone which itself is a polymer containing silicon, carbon hydrogen and oxygen.

Silicone rubber has many advantageous properties such as:

  • Generally non-reactive and stable
  • Resistant to extreme high and low temperatures, more so than many other polymers
  • Maintains flexibility over a wide temperature range.
  • It can be easily pigmented into a variety of colours.
  • Can provide effective thermal insulation.
  • Can reduce vibration and stabilise joins.
  • Resistant to UV and Ozone

Silicone has several advantages over EPDM including:

  • Generally, silicone can be utilised in a wider range of applications than EPDM.
  • Silicone can withstand a wider temperature range from -50°C to + 300°C.
  • Unlike EPDM, silicone does not shrink during heating. EPDM can shrink by approximately 50% when heated above 150°C.

EPDM has a higher mechanical strength than silicone and is more resistant to abrasion.

Silicone is resistant to UV and Ozone damage which can cause other types of rubber to fail. It is also resist to extremely hot and cold conditions as well as wet, dry and humid conditions.

Conventional grades of silicone rubber are not suitable for environments where they will come into contact with fuels, solvents and oils. However, fluorosilicone has excellent performance under these conditions.

Generally, silicone rubbers have poor resistance to steam and super-heated water. Steam-resistant grades of silicone are available which have improved performance.

Yes, general purpose grades of silicone supplied by Viking Extrusions are fully compliant with FDA regulation 21CFR177.2600, EC1935/2004 and are WRAS approved (Water Regulations Advisory Scheme) for contact with drinking water. General purpose grades of silicone are available from 20° Shore A to 80° shore A.

Pigments used in silicone can meet some or all of the above standards. If your project requires a pigmented silicone, please contact us to discuss your specific requirements.

Specialist grades of silicone rubber are commonly used for the production of baby bottle teats, due to their cleanliness, transparency and low extractable content.

Products made from silicone are not advised to be used in high traffic applications. High tear strength silicone compounds have a modest abrasion resistance when compared to other types of rubber.

Silicone itself does not support microbiological growth; it is suitable for use in most clean room environments.

Yes, silicone sponges are produced by the addition of a chemical blowing agent into the silicone compound. This releases gas during the extrusion process, causing bubbles to form in the silicone. These bubbles allow the production of soft silicone sponge which has the same temperature and environmental performance as solid silicone made from the same compound.

Yes, silicone can be submerged in both fresh and salt water for long periods of time without adverse effects.

Silicone rubber is not adversely affected by immersion in either fresh or salt water.

Most general-purpose silicone base compounds are translucent and can be pigmented to achieve a wide range of colours. Viking Extrusions are able to colour match to samples, and offer fluorescent, glow in the dark and metallic pigments.

Some specialist grades of silicone have an off-white natural colour and can only accept a limited range of pigments.

Yes, special thermochromic pigments can be blended into the silicone compound to allow it to change colour with temperature.

Silicone products are very difficult to paint. Some surface treatments can help but in general, silicones resist paint application.

Silicone does not support microbiological growth. However, through the use of special additives in the silicone compound it is possible to produce silicone products that will actively kill many bacteria types such as e-coli and MRSA.

Silicone compounds should be stored at a temperature of less than 30°C, in a dry environment away from direct sunlight and heat.

Silicone rubber is not considered as hazardous waste in both its cured and un-cured states. It can be disposed of in accordance with local waste disposal regulations.

Silicone is generally considered non-toxic, making an ideal material choice for many food and beverage processing applications.

Silicone has virtually no toxic effect in most environments and is considered a very safe polymer. Silicone is not considered as hazardous waste and can be disposed of in accordance with local waste disposal regulations.

The temperature range of general-purpose silicones is -50°C to +200°C. High temperature grades of silicone are available with operating temperatures up to 300°C. Low temperature grades are also available, with operating temperatures as low as -110°C.

The temperature range of general-purpose silicones is -50°C to +200°C. High temperature grades of silicone are available with operating temperatures up to 300°C. Low temperature grades are also available, with operating temperatures as low as -110°C.

Generally, silicone is not thermally conductive. However, specialist grades of silicone are available which contain additives to enable conduction of heat.

Silicone is generally electrically insulative. However, electrically conductive grades of silicone are also available.

Silicone is not inherently flame retardant, but the use of additives can create grades of silicone with flame retardant properties. Viking Extrusions manufacture parts using flame retardant grades of silicone developed specifically for use in the aerospace and rail industries.

Some grades of silicone are described as addition cured because the curing mechanism is from a catalyst reaction between component ingredients within the compound. The term addition cured is used as these components must be added together for the compound to cure. Addition cure compounds are supplied as one-, two- or three-part systems.

Curing time depends on several factors including, temperature, cure mechanism and the size and thickness of the part. A typical curing time for a compression moulded part is 5 minutes at 180°C.

Extruded silicone is post cured for 8 hours at 200°C.

Both terms essentially describe the same process – the transformation of the polymer into a cross-linked rubber.

The curing time of a silicone compound can be reduced to a certain degree by manipulating the following variables:

  • Temperature
  • Mould design
  • Processing method
  • Using an addition cured (platinum cured) compound over a peroxide cured compound.

Silicone rubbers can be bonded to a variety of other substrates including metals and plastics. Special primers, surface preparation techniques and adhesives are used to increase the strength of the bond.


Silicones or polysiloxane are polymers made up of siloxane. They are composed of a backbone containing repeating silicon-oxygen with organic groups bonded to the silicone. Organic groups can include one or more of the following types: hydride, hydroxyl, methyl, phenyl, trifluoropropyl and vinyl. These groups can be varied to fine tune the material’s properties.

Silicone is used across a multiple industry for a wide range of applications due to its stable, non-reactive nature and ability to withstand extreme temperatures and environmental conditions.

EPDM (Ethylene propylene diene monomer) is a synthetic rubber with many applications. EPDM has many advantageous properties including stability, strength, resistance to degradation from environmental factors. It is used widely to make extruded, moulded and CNC cut gaskets and seals.

The term elastomer is a combination of elastic and polymer and describes polymers that have elastic properties, such as silicone rubber. They are defined by generally low Young’s modulus and high failure strain when compared with other materials, meaning that the material deforms when a force is applied but returns to its original shape once the force is removed.

Silicone polymer is combined with catalyst and other additives to create silicone compounds with different properties for various applications.

Learn more about the materials we supply.

A material’s compression set is the permanent deformation remaining after removal of a force that was applied to it. Compression set is measured as percentage loss of the material’s original thickness. The lower the compression set the better the material is at resisting permanent deformation.

The generally irreversible curing process where rubber-like polymers under-go cross linking, giving them increased rigidity and durability.

Silicone rubber that has been manufactured into sheets or rolls via calendaring or moulding processes.

An alternative method to peroxide curing silicone. Platinum curing is often used to produce a final product with greater purity. Platinum curing has several advantages over peroxide cured silicone including higher elongation, better tear strength and higher clarity or transparency as no by-products are produced. These properties make platinum cured silicone suitable for use in medical applications and applications involving the inspection of fluids.

Silicone foam (or silicone sponge) is generally used to make gaskets, either via extrusion or cut from sheet. They are used to make seals to insulate and protect applications in a range of industries.

The process of exposing silicone to high temperatures for a selected period of time. This process drives of volatiles that remain from curing process and result in a more stable finished product.

Silicone is inert, non-reactive and non-toxic in nature, making it suitable for a variety of applications. Different grades of silicone are made to different specifications and regulations determined by their intended purpose. As a result, not all silicone products are suitable for all applications, as different curing agents and additives are used during their manufacture.

Visit our materials page for more information on the material grades we supply.

Silicone rubber is used widely in the food industry. Silicone can be supplied to meet food standards such as FDA 21 CFR 177.2600, BfR and EC1935/2004. Silicone’s inert and sterile properties make it safe for food contact when manufactured to the correct standards.

To learn more about the applications of silicone, visit our Food and Dairy page.

Silicone is not adversely affected by either fresh or salt water and can be submerged for prolonged periods of time, making it suitable for Marine applications. Silicone can be used in both freezing and boiling water without adverse effect.

Silicone rubber is a thermoset material, meaning once the material has been cross-linked it cannot be melted and reshaped.

Room temperature vulcanisation refers to a grades of silicone rubber that cure at room temperature. RTV’s are available in single component, or two-component mixes (a base and curative). They are supplied in liquid or semi liquid form and range from very soft (15 Shore A) to medium hardness (40 Shore A).

A high temperature vulcanisation (HTV) grade of silicone rubber is cured with the application of heat. Generally, these grades are supplied in a thick putty form and are suitable for compression moulding, transfer moulding and extrusion.

ISO Reference: 4649

Abrasion resistance refers to a material’s abrasion, which is a method of wearing down or rubbing away by means of friction. The ability to resist abrasion helps a material keep its original look and structure. Abrasion resistant materials are useful for moving and fixed parts where wearing is an issue.

Several different abrasion machines have been designed to measure abrasion resistance. Results are recorded either as volume loss per standard test piece or as the difference in volume loss compared with a standard material of known abrasion value.

ASTM Reference: D573

ISO Reference: 188

BS Reference: BS 903 Part A19


Heat ageing is a method that is widely used to evaluate the long-term ageing properties of a material.  Test pieces are placed in an air circulating oven at a set temperature for a specified time period. The properties of the rubber are tested before and after the heat ageing process. The comparison between the samples is measured as the percentage retained for each material property, apart from shore hardness, which is measured as change in degrees.

Commonly expressed as the change in certain properties (such as strength, hardness and elongation) caused by the presence of chemicals under defined test conditions (such as time, temperature and concentration).

 To learn more about the chemical compatibility of silicone and other rubbers view our chemical compatibility chart.

ISO Reference: 815

ASTM Reference: D395

The compression set of a material refers to the permanent deformation that remains once an applied force is removed. The compression set of a rubber is measured as the total height of a rubber sample that does not recover once the force is removed. It is expressed as a percentage of the total amount by which the material sample was compressed.

Premium grade elastomer sheeting with fabric reinforcement. For use primarily in diaphragm applications.

Diaphragms and flap values used in regulators, actuators, gas controls, pumps and metering equipment.

ISO Reference: 2878

ASTM Reference: D991 & D257

The dielectric strength of a silicone rubber (or other materials) is the maximum electrical field the material can withstand before undergoing electrical breakdown and conducting an electrical current i.e., it is a measure of failure of a material’s electrical insulation properties.

ASTM Reference: D412

ISO Reference: 37

Elongation at break is defined as the percentage increase in length that a material can achieve before breaking.  For example, if a rubber can reach twice its original length before breaking its elongation would be 100%.

Flame resistance testing involves igniting a rubber sample of a specified size with a flame for a set period of time. The flame is then removed. The time taken for the rubber to self-extinguish is then recorded with notes taken on hot particles emitted and afterglow.  To be classed as flame resistant a silicone rubber must self-extinguish within a specified time.


Visit our materials page to learn more about the flame-retardant silicone grades we supply.

BS Reference: BS 903 Part A16

ISO Reference: 1817

ASTM Reference: D471

Volume swell testing records the deterioration of silicone (or other rubbers) when exposed to fluid through measuring the change in the material’s volume. It is usually expressed as a percentage of the original volume.

Rubber components used in a variety of industrial applications such as aerospace, automotive and oil and gas are exposed to liquids which can cause volume swell impacting the performance and service life of the component.

ASTM Reference: D2240 & D1415

ISO Reference:  48


The shore hardness of a rubber is a measure of its resistance to indentation. Shore hardness is measured in degrees and there are three commonly used sales Shore A, Shore D and IRHD (International Rubber Hardness Degrees).

As default Viking Extrusions uses the Shore A scale of measurement.

Moulded seals made from silicone rubber. Available in small or high volume, for use in industries such as food processing, medical and automotive.

For more information on our moulding capabilities, visit our following pages: compression moulding, injection moulding, 3D printed silicone moulds.

ASTM Reference: D1149

ISO Reference: 1431-1

Ozone can cause cracking in rubber. To measure Ozone resistance, test pieces are usually placed under a small degree of tension. This can be done either by bending around a mandrel or stretching by 5%. The test sample is then exposed to a controlled atmosphere under static conditions. Cracks are graded by photograph, measurement or description. Results may be presented as the grade of cracking after a fixed period of time, or the time taken to reach a set degree of cracking.

ASTM Reference: D624

ISO Reference: 34


Tear strength (or tear resistance) is a measure of how well a material can withstand the effects of tearing. Tear resistance is measured as how a test specimen of material resists the growth of any tears when placed under tension. Tear strength is usually measured in kN/m.

ASTM Reference: D412

ISO Reference: 37


Tensile strength is a measurement of the force required to pull a material specimen to the point where it breaks. For rubbers, this is usually a standard dumbbell type test piece. The tensile strength is recorded as force per unit area.

A material’s thermal conductivity is a measure of its ability to conduct heat. Heat transfer occurs at a higher rate in materials with high thermal conductivity than in materials with low thermal conductivity. For example metals would generally be considered good conductors with high thermal conductivity, whereas rubbers are generally good insulators with low thermal conductivity.

Viton is a brand of FKM (a synthetic fluoropolymer elastomer). The name is a registered trademark of Du Pont. Viton is characterised by its resistance to high temperatures, its resistance to chemicals (including oils, acids, silicone fluids and aromatic hydrocarbons) and extreme environmental conditions.

Vulcanised joined rings are made from extruded profiles, cords and tubes which are cut to the required length and then vulcanised to create a ring. Vulcanise joined rings are used widely for sealing applications.

ASTM Reference: D1171

ISO Reference: 4665

Weather resistance testing involves measuring. The properties of test pieces before and after exposure and changes in mechanical properties are expressed in percentage terms (with exception to shore hardness which is measured in degrees). Weather resistance can be a subjective test and it is important to accurately state conditions in which the exposure took place such as geographic location, dates etc.