Liquid silicone rubber: complete guide to properties, uses & selection

What is liquid silicone rubber?

Liquid silicone rubber is a two-component, platinum cured silicone elastomer material processed via injection moulding, offering a continuous operating temperature range of −60 °C to +250 °C. Unlike conventional rubber compounds, it begins as a flowable liquid and crosslinks under heat into a durable, flexible elastomer — making it fundamentally different from compression moulding rubber or thermally processed thermoplastic elastomer systems.

Liquid silicone rubber is defined as: a platinum cured, two-component silicone system in which Part A (containing the vinyl-functional polymer and platinum catalyst) and Part B (containing the crosslinker) are metered, mixed, and injected into a heated mould cavity where vulcanisation occurs rapidly and completely. The result is a biocompatible silicone component with outstanding dimensional stability, low shrinkage, and consistent mechanical properties across production runs.

Why do so many engineers still confuse LSR with standard "silicone"? The distinction matters enormously. Much of what the market calls "silicone rubber" is actually high consistency rubber (HCR) — a dough-like compound processed by compression moulding rubber techniques. LSR, by contrast, is a liquid system optimised for automated liquid injection moulding. The processing temperatures, tooling requirements, cycle times, and achievable tolerances are simply not comparable.

According to recent 2026 data from Grand View Research, the global LSR market was valued at approximately £2.8 billion in 2023 and is projected to reach £4.6 billion by 2030, driven primarily by medical, automotive and consumer electronics demand. Medical grade silicone and food grade silicone rubber applications together account for over 40% of downstream consumption.

For a detailed technical overview, the Liquid Silicone Rubber – Overview and Properties reference provides a useful starting point for understanding the chemistry underpinning LSR systems.

How does LSR differ from other silicone types?

LSR sits within the broader silicone rubber family but occupies a distinct processing niche. Room temperature vulcanising (RTV) silicones cure at ambient temperature and are used primarily for sealing, potting and mould-making. HCR requires milling and compression or transfer moulding. LSR alone is suited to fully automated, closed-loop injection moulding with flash-free tooling — enabling part complexity and volume efficiency that neither RTV nor HCR can match.

What industries rely on liquid silicone rubber?

Medical device manufacturers, automotive OEMs, infant product brands, food processing equipment producers, and electronics companies all rely on LSR. The material's biocompatible silicone profile, combined with its chemical inertness and sterilisation compatibility, makes it irreplaceable in applications where both safety certification and long-term performance are non-negotiable.

LSR properties and Shore A hardness guide

The mechanical and thermal profile of liquid silicone rubber is what sets it apart from nearly every competing flexible rubber compound. Understanding these properties — and how they vary with formulation — is the foundation of sound material selection.

Core physical and thermal properties

LSR maintains its elastic properties across an exceptional temperature range, remaining functional from −60 °C to +250 °C without hardening or embrittling. Tensile strength typically ranges from 4 MPa to 12 MPa depending on formulation, with elongation at break values between 200% and 800%. Tear strength, compression set resistance, and UV stability are all substantially superior to organic rubber systems such as EPDM or natural rubber. Electrically, LSR behaves as a reliable silicone gasket material and insulating compound, with volume resistivity commonly exceeding 10¹⁴ Ω·cm.

Actual testing data from moulding trials consistently confirms one critical property: LSR's compression set under prolonged loading remains very low — typically below 15% after 22 hours at 175 °C under 25% deflection. For dynamic sealing applications, this performance simply cannot be replicated by a thermoplastic elastomer at elevated temperatures.

Shore A hardness grades and application mapping

Shore A hardness is the primary specification variable for LSR procurement. Grades typically span from 10 Shore A (extremely soft, gel-like) through to 80 Shore A (firm, structural). The table below maps hardness grades to typical applications — a reference that competing guides consistently omit.

Of course, hardness alone does not determine suitability. Tear resistance, elongation, and post-cure shrinkage must all be evaluated in context. A 40 Shore A medical grade silicone formulation behaves very differently from a general-purpose 40 Shore A grade if one has been optimised for biocompatibility testing under ISO 10993.

LSR injection moulding process explained

LSR injection moulding is a highly controlled, automated process that consistently delivers tight-tolerance components at production scale. Understanding each stage helps procurement managers communicate effectively with toolmakers and moulders.

Step-by-step LSR injection moulding process

1. Material preparation: Part A and Part B of the two-component silicone system are stored in separate drums and connected to a metering unit that delivers a precise 1:1 ratio by volume.
2. Metering and mixing: The two components pass through a static or dynamic mixer, achieving homogeneous dispersion of catalyst and crosslinker without introducing air voids.
3. Cold runner injection: The mixed material is kept below 10 °C in the cold runner system to prevent premature vulcanisation before it enters the heated mould cavity.
4. Mould filling and curing: The mould is held at 160–220 °C; the platinum catalyst initiates rapid addition-cure crosslinking, with typical cycle times of 15–60 seconds depending on wall thickness and part geometry.
5. Demoulding: Flash-free, precision-tooled moulds allow automated demoulding; silicone overmoulding onto engineering plastics can occur in the same cycle using self-adhesive LSR grades.
6. Post-cure (optional): A secondary oven post-cure at 200 °C for 1–4 hours removes residual volatile cyclic siloxanes, which is mandatory for most medical grade silicone and food grade silicone rubber applications.

Cold deck tooling and automation advantages

The cold runner system is what makes LSR injection moulding economically viable at high volumes. Unlike thermoplastic injection moulding, there is no sprue or runner waste — the material remaining in the cold manifold is simply held in liquid form for the next shot. For a typical automotive connector programme producing 500,000 parts per year, this zero-waste characteristic produces measurable material cost savings. Real-world tooling projects in the UK automotive sector have demonstrated material yield efficiencies exceeding 98% with well-designed cold deck systems.

Industry leader guidance from Silicone Materials and Liquid Silicone Rubber Solutions by Elkem reinforces that material selection, mould design, and processing parameters must be developed in parallel for LSR programmes to achieve the dimensional accuracy that liquid injection moulding is capable of delivering.

LSR vs TPE, EPDM and high consistency rubber

Material selection at the engineering stage is rarely straightforward. LSR competes directly with thermoplastic elastomer (TPE), EPDM rubber, and high consistency rubber (HCR) across multiple applications. The differences are significant — and choosing the wrong material can mean tooling rework, regulatory non-compliance, or premature field failure.

"The selection between liquid silicone rubber and thermoplastic elastomers must be driven by the application's thermal, chemical and regulatory demands — not by unit price alone. LSR's long-term performance in aggressive environments consistently justifies its higher tooling investment." — Industry consensus across major elastomer material suppliers, 2026.

Multi-dimensional material comparison

When to choose LSR over its alternatives

If your application demands sterilisation compatibility, wide thermal cycling, and regulatory documentation for a medical or food contact context, LSR is almost always the correct choice. TPE, though recyclable and lower in tooling cost, cannot match LSR's performance above 120 °C or in environments with sustained chemical exposure. EPDM remains competitive for outdoor sealing applications where biocompatibility is not required. HCR is often the pragmatic choice for large cross-section extrusions or low-volume parts where the capital cost of LSR injection moulding tooling cannot be justified.

Key applications across industries

Liquid silicone rubber has become the default elastomer of choice wherever precision, safety and durability intersect. Its application map spans multiple sectors, each placing different demands on material formulation and processing.

Medical and healthcare

Medical grade silicone is the dominant sub-category in healthcare. LSR is used in catheters, drainage tubes, respiratory masks, hearing aid components, implantable seals and wearable monitoring device interfaces. The material's biocompatible silicone characteristics — specifically its inertness, sterilisation tolerance (autoclave, EtO, gamma), and proven ISO 10993 and USP Class VI test records — make it the benchmark elastomer material for any body-contacting application. In 2026, the push toward ultra-thin-wall (<0.3 mm) medical wearables has placed new demands on LSR formulations and moulding precision, with self-adhesive grades enabling direct silicone overmoulding onto polycarbonate housings without a primer layer.

Food contact and infant products

Food grade silicone rubber for valves, tubing, baking moulds and infant feeding products represents one of the most recognisable consumer applications. In the UK market, compliance with both FDA 21 CFR 177.2600 and UK Food Standards Agency (FSA) guidelines is required for food-contact components. Infant items — teats, soothers, bottle nipples — require additional compliance with EN 1400 and specific migration testing. LSR's odourless, non-toxic, and heat-stable profile is simply unmatched by competing flexible rubber compounds in this context.

Automotive and electronics

Connector seals, grommet assemblies, spark plug boots and sensor housings all use LSR because its silicone gasket material properties remain stable throughout the thermal cycling and vibration loads typical of automotive environments. In electronics, LSR is used for keyboard membranes, LED optical elements (optical grade LSR, with >90% light transmittance), and sealing components in IP67/IP68 assemblies. The material's electrical insulation properties, combined with flame-retardant LSR variants compliant with UL94 V-0, make it a reliable choice for power electronics enclosures and new energy vehicle battery systems.

UK compliance: UKCA, CE and regulatory requirements

Post-Brexit regulatory divergence is one of the most practically important — and least discussed — dimensions of sourcing LSR in the UK. Getting this wrong has serious commercial and legal consequences.

UKCA marking and the post-Brexit regulatory landscape

Since 1 January 2021, products placed on the Great Britain market (England, Scotland, Wales) require UKCA marking rather than CE marking for most regulated product categories. For LSR components used in medical devices, this means compliance with the UK MDR 2002 (as amended) and registration with the MHRA, rather than relying on EU MDR 2017/745 CE certification alone. Northern Ireland retains CE marking requirements under the Windsor Framework, creating a dual-compliance scenario for manufacturers supplying both markets. Engineering procurement teams evaluating LSR suppliers should explicitly confirm whether the supplier's material documentation and test data support UKCA as well as CE conformity.

Relevant UK and international standards for LSR

Key standards governing LSR materials and their applications in the UK include ISO 10993 (biological evaluation of medical devices), ISO 13485 (quality management for medical devices), BS EN 1400 (infant soothers), and UK REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals). Food contact applications must comply with UK FSA guidance derived from EU Regulation 10/2011, though the UK has retained equivalent provisions post-Brexit. The ISO Standards for Silicone Rubber Materials provide the internationally recognised test methodologies that underpin material qualification documents.

From a material chemistry standpoint, RoHS compliance is relevant for LSR used in electrical and electronic equipment — confirming the absence of restricted hazardous substances including lead, cadmium and certain phthalates. Reputable LSR suppliers active in the UK market will hold current RoHS declarations of conformity alongside FDA, REACH SVHC screening reports, and ISO 10993 biocompatibility dossiers. The broader silicone elastomer landscape, including regulatory context, is well documented by Silicone Elastomers including Liquid Silicone Rubber from DuPont's technical library.

Practical compliance checklist for UK procurement teams

Before approving an LSR grade for a regulated application, procurement managers should request: a full material safety data sheet (MSDS/SDS), ISO 10993 biocompatibility summary (for medical/food contact), REACH SVHC declaration, RoHS declaration, FDA 21 CFR compliance letter (if applicable), and — crucially — confirmation of UKCA-compatible documentation for GB market placement. Do not assume CE-certified materials automatically satisfy UKCA requirements; the conformity assessment routes and notified body equivalence differ.

Sustainability and environmental considerations

Environmental scrutiny of materials has intensified considerably in 2026. LSR presents an interesting sustainability profile — genuinely strong in some dimensions, and more nuanced in others. Honest evaluation requires acknowledging both.

Lifecycle assessment and durability advantages

Thermoset materials like liquid silicone rubber cannot be melted and remoulded in the way a thermoplastic elastomer can, which is a genuine limitation from a circular economy perspective. However, LSR's exceptional durability significantly extends product service life — a medical grade silicone seal that outlasts three generations of its EPDM equivalent contributes a net lifecycle benefit when assessed on a per-service-year basis. Life cycle assessment (LCA) studies have increasingly demonstrated that the manufacturing energy and emissions embedded in a long-life LSR component can be substantially lower per functional unit than shorter-life alternatives when replacement frequency is factored in.

LSR recyclability, RoHS and UK regulatory alignment

Direct mechanical recycling of cured LSR is not commercially viable at scale, though chemical depolymerisation pathways are under active development by silicone producers including Elkem and Wacker. Ground LSR waste (LSR regrind) can be used as a filler or additive in lower-specification applications. From a chemical safety standpoint, platinum cured silicone contains no peroxide residues, no heavy metal catalysts relevant to RoHS restrictions, and is inherently free of the phthalate plasticisers that create concerns in PVC-based flexible compounds. UK RoHS 2013 (SI 2013/3032, as amended) compliance is straightforwardly achievable for standard LSR formulations, giving procurement teams a clean regulatory baseline. The emergence of low-volatile LSR grades — formulated to minimise cyclic siloxane (D4/D5) emissions — directly addresses REACH SVHC restrictions and is a 2026 procurement priority for sustainability-conscious UK manufacturers.

How to choose an LSR supplier in the UK

With material quality, regulatory documentation, and processing capability all intertwined, supplier selection for liquid silicone rubber is a multi-dimensional decision — not a simple price comparison exercise. What separates a competent LSR partner from a generic rubber moulder? The answer lies in process control, certification depth, and technical collaboration capability.

Criteria for evaluating LSR moulding partners

Based on real-world supplier qualification programmes, the following criteria consistently differentiate high-performing LSR partners. ISO 13485 certification signals genuine medical device manufacturing discipline beyond baseline ISO 9001 quality systems. Cold runner tooling capability — not just conventional compression moulding rubber presses — is essential for precision LSR parts. Process validation documentation (IQ/OQ/PQ protocols) is non-negotiable for regulated applications. The ability to offer silicone overmoulding, two-component silicone insert moulding, and secondary post-cure infrastructure within a single facility reduces supply chain complexity considerably. Ask directly about their experience with thin-wall geometries below 0.5 mm, as this is a reliable proxy for overall LSR process maturity.

UK market considerations and regional suppliers

The UK LSR processing sector includes specialist moulders concentrated in the Midlands, South West and Scotland. While the material itself is typically sourced from global producers — Elkem, Wacker, DuPont and Shin-Etsu are the principal LSR raw material suppliers active in the UK market — the conversion (moulding) capability is largely domestically distributed. Post-Brexit, nearshoring of critical component supply has become a strategic priority for many UK OEMs, and domestic LSR moulding capacity has seen investment accordingly. When comparing UK-based and imported LSR components, factor in: lead time risk, UKCA documentation accountability, language clarity in technical communication, and the practical ease of conducting mould trials and design reviews. Price differential between UK and Asian sources has narrowed in recent periods when total landed cost, quality rework risk, and minimum order quantities are properly accounted for.

For deeper reference on material specifications and supplier capability benchmarks, the Silicone Materials and Liquid Silicone Rubber Solutions technical documentation from Elkem provides a useful independent standard against which to evaluate supplier claims.

In summary, liquid silicone rubber remains one of the most technically capable elastomer materials available to UK engineers and procurement teams in 2026. Its combination of biocompatible silicone properties, thermal range, processing precision via liquid injection moulding, and regulatory tractability across UKCA, FDA and ISO frameworks makes it the material of choice wherever performance and compliance are both critical. The investment — in tooling, validation and supplier qualification — is real. But so is the return.