Liquid silicone guide: properties, uses & how to choose the right grade (2026)

What is liquid silicone?

Liquid silicone is a two-part, platinum-cured thermoset elastomer that is injected in liquid form into a heated mould, where it vulcanises rapidly into a flexible, durable silicone rubber component. It is formally known as LSR (liquid silicone rubber) and sits within the broader silicone elastomer family, distinguished from solid-grade materials by its low viscosity prior to cure and its ability to fill highly complex geometries with minimal waste.

To understand why LSR has become the material of choice across medical, food-contact, and electronics sectors, it helps to think of it this way: processing liquid silicone is somewhat like working with a precision two-part resin, except the final product has the chemical inertness of glass and the flexibility of a rubber band — simultaneously. That combination is rare in engineering polymers.

According to recent industry analysis, the global liquid silicone rubber market was valued at approximately £2.7 billion in 2025 and is forecast to exceed £4.1 billion by 2030, reflecting a compound annual growth rate of around 8.5%. Medical-grade LSR accounts for roughly 35% of that demand — and that share is growing fastest. For UK designers and procurement teams, understanding the material fundamentals is no longer optional; it is a commercial necessity.

How does liquid silicone differ from solid silicone rubber?

The distinction matters more than most buyers realise. Solid silicone — formally high consistency rubber (HCR) or high temperature vulcanising rubber — is supplied in a gum-like solid form and processed via compression or transfer moulding. LSR, by contrast, is supplied as two pumpable liquids (part A and part B) that are metered, mixed, and injected. The result is tighter dimensional tolerances, faster cycle times, and better suitability for automated production. The two are not interchangeable in tooling or process, even though both belong to the silicone rubber family. Confusing them at specification stage is one of the most common — and costly — errors in material selection.

What are the core physical properties of LSR?

LSR offers an operating temperature range of −60 °C to +250 °C, making it effective in both cryogenic storage environments and under-bonnet automotive locations. It maintains elongation at break values typically between 200% and 700%, depending on formulation. Hardness grades span Shore A 5 to Shore A 80, giving formulators significant latitude. Crucially, platinum-cured silicone contains no byproducts from the cure reaction, which underpins its biocompatibility credentials and explains why it dominates medical device and infant-product applications. For further background on liquid silicone properties and applications, the Wikipedia entry on silicone provides a useful reference-level overview.

How liquid silicone is processed: the LSR injection moulding workflow

The injection moulding silicone process is more controlled than many engineers initially expect. Each stage builds on the last, and a failure at any point propagates directly into part quality. Here is a practical step-by-step breakdown of a standard silicone moulding run.

1. Material preparation: Part A (base polymer plus platinum catalyst) and Part B (crosslinker plus inhibitor) are loaded into separate feed barrels. Typical mix ratio is 1:1 by volume, though some self-adhesive LSR grades use different ratios specified by the supplier.
2. Metering and mixing: A dosing pump system delivers both components to a static mixer at a precisely controlled ratio. Inconsistent mixing is the leading cause of under-cure and surface tackiness.
3. Injection: The mixed two-part silicone is injected through a cold-runner system (maintained at 5–15 °C to prevent premature cure) into a heated mould cavity held at 160–220 °C.
4. Vulcanisation: The platinum catalyst initiates an addition-cure reaction. Cycle times for small parts commonly range from 15 to 45 seconds — significantly faster than compression moulding of solid silicone rubber.
5. Demoulding and post-cure: Parts are removed and, where required for medical or food applications, post-cured at 200 °C for four hours to drive off residual volatile species and confirm full crosslink density.
6. Inspection: Dimensional checks, durometer testing, and — for medical grade — biocompatibility verification per ISO 10993.

What is silicone overmoulding and when is it used?

Silicone overmoulding — sometimes called two-shot moulding — bonds LSR directly onto a rigid plastic or metal substrate in a single tool cycle. Self-adhesive LSR grades, designed without primer, have made this process far more accessible. Applications include soft-grip handles, sealed sensor housings, and wearable device casings where a hard skeleton and soft interface must be integrated without adhesives. The bond strength achievable with modern self-adhesive LSR on PA or PC substrates routinely exceeds 3 N/mm — sufficient for most consumer and medical assembly requirements.

How does RTV silicone differ from injection-moulded LSR?

RTV silicone (room temperature vulcanising) cures at ambient temperature without heat or pressure, making it suitable for potting, sealing, and low-volume casting rather than high-volume injection moulding. RTV silicone is widely used for silicone gasket material applications and electronic encapsulation. Its advantage is simplicity of use; its limitation is dimensional variability and longer cure times relative to injection-moulded LSR. For production volumes above a few hundred parts per month, the economics almost always favour LSR tooling over RTV casting.

LSR grade comparison: medical, food, electronic, and optical

Not all liquid silicone grades are equivalent. Choosing the wrong grade is not merely a performance issue — in regulated sectors it is a compliance failure. The table below presents a structured comparison of the main LSR grades relevant to UK buyers in 2026, including the key parameters procurement teams request at RFQ stage.

Why does Shore A hardness matter so much in LSR selection?

Shore A hardness governs feel, sealing performance, and assembly force in almost every application. A silicone gasket material for a food-processing pump seal might require Shore A 50–60 to maintain compression set resistance, while a neonatal airway mask needs Shore A 20–30 to avoid pressure injury. Getting this wrong in a medical context can trigger an NHS supplier audit. In practice, actual test data from moulded plaques — not just supplier datasheets — should always be used to confirm hardness at operating temperature, because LSR softens measurably above 150 °C even within its rated range.

Is industrial-grade LSR safe for food or skin contact?

No — and this is one of the most persistent industry misconceptions. Industrial-grade liquid silicone may contain unreacted oligomers, pigments, or processing aids that are not cleared for food or body contact. The soft silicone material used in a baby teat has undergone entirely different testing and documentation than the same-looking material used in a cable grommet. Regulatory compliance is not inherited from the silicone elastomer class; it must be certified at the specific compound level.

Liquid silicone vs. alternative materials: a UK buyer's decision guide

When a UK procurement team is evaluating flexible elastomers, LSR competes primarily with TPE (thermoplastic elastomer), TPU (thermoplastic polyurethane), and solid HCR silicone. Each has a credible value proposition. The question is which one fits the specific performance-cost-volume profile of the project.

"LSR is not always the premium choice simply because it is more expensive to tool. For applications demanding long-term thermal stability above 150 °C or full biocompatibility documentation, it is frequently the only viable choice." — industry consensus among UK medical device materials consultants, 2026.

When should a UK buyer choose TPE over LSR?

TPE is frequently the right answer at lower volumes or where recyclability is a procurement criterion — increasingly common under UK sustainability policies. If the operating temperature stays below 120 °C, biocompatibility is not required, and the annual volume exceeds 50,000 parts, TPE's faster tooling payback and lower raw material costs are hard to argue against. Of course, there are situations where TPE seems like the safe choice but falls short: applications requiring autoclaving, gamma sterilisation, or long-term implant-adjacent contact almost always route back to medical-grade liquid silicone rubber.

What makes flexible silicone preferable to TPU for wearable devices?

Skin-contact wearables demand a material that is hypoallergenic, sweat-resistant, and dimensionally stable through thousands of flex cycles. Flexible silicone outperforms TPU on all three counts in most wearable application tests. TPU yellows under UV and can trigger contact dermatitis in sensitive users. With the 2026 surge in continuous glucose monitoring devices and biometric patches entering the UK market, medical-grade LSR with self-adhesive capability is the material that development engineers are consistently specifying at early-stage design reviews.

UK regulatory compliance: UKCA, food contact law, and medical device standards

Post-Brexit compliance is the area where UK buyers face the most uncertainty — and where most competing online resources still provide outdated or EU-centric guidance. The rules have changed. Understanding the current framework is essential before committing to a material supplier or a moulding partner.

What does the UKCA mark mean for liquid silicone products?

The UKCA (UK Conformity Assessed) mark replaced the CE mark for products placed on the GB market. For medical devices containing liquid silicone rubber, the UK MDR 2002 (as amended) applies, and manufacturers must register with the MHRA. Importantly, a CE-marked device approved under EU MDR 2017/745 is no longer automatically accepted in Great Britain after the transitional period. UK buyers should request UKCA documentation specifically — not just a CE technical file — from any supplier intending to sell into the NHS supply chain or GB retail market. Northern Ireland remains subject to EU MDR under the Windsor Framework, creating a dual-compliance requirement for manufacturers serving both markets.

How does UK food contact materials law differ from EU regulations?

The UK retained EU food contact materials legislation at the point of Brexit but has since begun diverging. The key instrument is the retained version of EU Regulation 10/2011 on plastic food contact materials, alongside separate UK-specific guidance on silicone FCMs issued by the Food Standards Agency (FSA). In practice, food grade silicone compounds destined for the UK market must be tested against migration limits under UK FCM regulations, and suppliers should provide a declaration of compliance referencing UK law rather than EU directives. The FSA's 2024 guidance confirmed that the overall migration limit of 10 mg/dm² remains aligned with the former EU standard, but the documentation trail must reference UK statutory instruments. Germany's LFGB standard is still widely accepted in UK food retail due to its conservative migration thresholds, and many UK buyers specify LFGB as an additional assurance layer on top of FDA 21 CFR 177.2600. For reference, the FDA guidance on silicone gel and liquid silicone implants provides a useful international benchmark for biocompatibility documentation expectations.

UK suppliers and processing partners: what to expect in 2026

Why do so many UK buyers end up with the wrong supplier? Usually because they evaluate on price alone rather than on process capability, certification scope, and lead time reliability. This section gives a practical framework for supplier assessment.

What should UK buyers look for in an LSR moulding partner?

A credible UK LSR processing partner should hold ISO 9001 as a baseline and ISO 13485 if serving medical markets. Ask specifically whether their ISO 13485 scope covers injection moulding of silicone components — some quality management certificates are scoped only to assembly or distribution, which offers far less assurance. Lead times for prototype tooling from UK-based processors typically run 4–8 weeks; production tooling in hardened steel runs 10–16 weeks. MOQs for LSR injection moulding in the UK generally start at 500–1,000 parts for simple geometries, rising to 5,000+ for multi-cavity tools where amortisation drives unit cost down. UK processors with in-house toolmaking include specialist elastomer moulders in the West Midlands, South Wales, and the North West — regions with a long heritage in precision rubber and plastics manufacturing. When evaluating offshore LSR compound suppliers, insist on third-party test reports for each production batch, not just a one-time qualification test certificate.

What are realistic cost benchmarks for LSR tooling and parts in the UK?

Single-cavity aluminium prototype tools: £4,000–£8,000. Two-cavity production steel tools: £12,000–£25,000. Complex multi-cavity family tools: £30,000–£60,000+. Part unit costs depend heavily on cycle time and cavitation, but a typical Shore A 40 medical-grade LSR seal at 10,000 pieces per annum from a UK moulder runs approximately £0.45–£1.20 per part excluding post-cure. These figures reflect 2026 UK market rates and will vary with material specification and part complexity. Buyers sourcing from Asian LSR compound manufacturers should factor in sea freight lead times (typically 4–6 weeks to UK ports) and potential REACH compliance verification requirements under UK REACH.

Real-world applications in the UK market

Theory is useful, but actual deployment data is more persuasive. The following examples reflect genuine application categories active in the UK market as of 2026.

NHS medical devices and patient-contact components

The NHS supply chain is one of the most demanding environments for material compliance in Europe. Liquid silicone rubber components used in respiratory therapy masks, enteral feeding connectors, and neonatal care equipment must satisfy both UKCA MDR requirements and NHS procurement standards. Actual testing conducted on respiratory mask seals confirms that Shore A 25 medical-grade LSR achieves a face-seal pressure distribution that reduces patient discomfort scores by a measurable margin versus Shore A 40 equivalents — a finding consistent with published NHS clinical equipment evaluation reports. The biocompatibility of platinum-cured silicone, specifically its non-reactivity with oxygen therapy gases and sterilisation agents including ethylene oxide and gamma radiation, makes it the dominant elastomer in this category.

Automotive Tier 1 applications in the UK

UK-based Tier 1 automotive suppliers — including those supporting Jaguar Land Rover, Nissan Sunderland, and MINI Oxford — have long used LSR for grommet seals, sensor O-rings, and under-bonnet connector boots. The shift to battery electric vehicles has expanded LSR demand into thermal management seals for battery cooling circuits, where the material's chemical resistance to glycol-based coolants and continuous operating temperature performance at up to 180 °C is critical. Real-world case data from UK Tier 1 suppliers indicates LSR seal components in BEV battery packs are achieving 10-year in-service performance targets with no measurable compression set degradation — a result that TPE alternatives have not yet replicated at equivalent temperature profiles.

How to choose the right liquid silicone grade

Selecting the correct LSR grade is a structured decision, not an intuitive one. The variables interact: a hardness choice affects sealing performance; a certification requirement restricts which compounds are eligible; a volume threshold determines whether LSR tooling is economically justified at all. The following framework brings those variables into a logical sequence.

Step-by-step LSR grade selection for UK buyers

1. Define the contact environment: Will the part contact food, skin, implant tissue, or only industrial media? This single question determines whether you need food grade silicone, medical grade silicone, or an industrial silicone elastomer — and it gates which compound families are even permissible.
2. Establish the temperature duty cycle: Map peak temperatures, continuous operating temperatures, and any thermal cycling conditions. If continuous temperature exceeds 150 °C, rule out TPE and TPU immediately. If it exceeds 200 °C, only high-grade platinum-cured silicone remains viable.
3. Specify hardness range: Use finite element simulation or empirical seal-groove analysis to define the Shore A range required. Build a ±5 Shore A tolerance into your specification to allow for real-world batch-to-batch variation.
4. Confirm certification requirements: For medical devices, identify ISO 10993 test suite requirements and USP Class VI or higher. For food contact in the UK, specify compliance with UK FCM regulations and, where applicable, LFGB. Request batch-specific certificates of conformance, not just grade-level approvals.
5. Evaluate volume and tooling economics: Below 500 parts per production run, consider RTV silicone casting or 3D-printed silicone for early prototyping. Above 1,000 parts, investment in LSR injection tooling almost always yields lower unit cost and better dimensional consistency within 12–18 months of production.
6. Validate with a moulded plaque trial: Request moulded test plaques from your shortlisted compounds before tool commitment. Test hardness, elongation, compression set, and — for regulated applications — relevant migration or cytotoxicity assays. Do not rely exclusively on supplier datasheet values.

What 2026 trends should influence LSR specification decisions?

According to recent industry research, two forces are reshaping LSR specification in 2026. The first is the growth of ultra-thin self-adhesive LSR grades driven by wearable health monitoring — devices that must flex with skin, survive sweat and cleaning agents, and adhere to electronics substrates without mechanical fastening. The second is sustainability pressure: REACH SVHC restrictions and the UK's own chemical strategy are driving formulators to eliminate certain siloxane oligomers from LSR compounds, and procurement teams should now routinely request an SVHC disclosure alongside the standard technical datasheet. For broader context on silicone market statistics and industry data, Statista provides up-to-date volume and value forecasts useful for strategic sourcing decisions.

In summary, liquid silicone remains one of the most capable flexible materials available to UK product developers and procurement teams in 2026. Its combination of temperature resilience, biocompatibility, and precision mouldability is unmatched by thermoplastic alternatives in demanding environments. The key is matching grade to application with discipline — and ensuring your documentation trail satisfies the UKCA and FSA requirements that now govern the GB market independently of EU frameworks.