LSR vs TPE: How to Tell Liquid Silicone from TPE — and Which One to Specify

2026-10-08 · 8 min read · Materials · Silicone · TPE · Sourcing

If you remember one thing from this page, remember this: LSR sinks, TPE floats. Liquid silicone rubber has a density of roughly 1.1 g/cm³ — heavier than water. TPE sits at about 0.9 g/cm³ — lighter. Drop a sample into a glass of water and the question answers itself in ten seconds.

Everything below is the detail behind that one test, plus the three other checks worth running and the commercial question underneath all of them: is it worth paying two to three times more for silicone?

Why this question keeps coming up

Because the two materials are genuinely hard to tell apart by eye. In photographs and video they look the same. They mould into the same shapes, take the same colours, and — on a good day — can be made to feel similar in the hand. Buyers who are new to the category, and end consumers with no reason to know better, routinely mistake one for the other.

The smell test that people rely on is also getting weaker. Pellet manufacturers have put real effort into suppressing the odour of TPE, and the latest compounding work has reduced it substantially. That is a genuine material improvement — but it means a weak nose is no longer a reliable instrument, and it is one more reason to base a sourcing decision on measured properties instead of a sniff.

Four tests you can run on a sample today

1. The water test — density

Fill a glass with water and drop the sample in.

• It sinks → the material is denser than water, which points to silicone (LSR, ~1.1 g/cm³).
• It floats → the material is lighter than water, which points to TPE (~0.9 g/cm³).

This is the fastest and most reliable field test, because density is a bulk property: it cannot be faked by a surface treatment, a coating, or a clever finish.

2. The heat test — where the two diverge sharply

This is the single biggest behavioural gap between the materials:

• TPE begins to soften and deform once its surface temperature passes roughly 60 °C.
• LSR does not soften at that temperature. It remains dimensionally stable even in environments around 200 °C.

In practice this decides a lot of applications. Anything that will be washed hot, stored in a warm vehicle, exposed to direct sun for long periods, or sterilised is asking for trouble in TPE. The same is true of any product where a softened surface means a failed product rather than a merely warm one.

A flame test will also separate them, but it destroys the sample and the interpretation depends on how you read the burning behaviour — the water test and the heat test give you a cleaner answer for less effort.

3. The smell test — useful, but no longer decisive

LSR does not give off an odour. TPE traditionally does — the sharp, chemical smell most people associate with cheap flexible plastic. That said, as noted above, modern TPE grades have been formulated to suppress this considerably.

Use smell as a supporting signal, not as your verdict. If a sample smells strongly, it is very likely TPE. If it is odourless, it may be silicone — or it may be a well-formulated TPE.

4. The ageing test — the slow one that matters most

LSR is colourless, odourless and stable in storage. Left alone for years, it stays what it was.

TPE does not. Over time it tends to drift in colour and distort in shape. For a product with a shelf life, or one that a consumer will keep for years, this is often the decisive factor — and it is the one you cannot test in an afternoon.

The two materials side by side

Where TPE genuinely wins

It would be dishonest to present TPE as simply the cheaper, worse option. It is a competent material with real advantages:

• Cost — and this is about more than the sticker price. Per kilogram, TPE pellets run roughly two to three times cheaper than LSR. On top of that, TPE is a thermoplastic: it can be melted and re-melted, so sprues and rejected parts go straight back into the machine. Material utilisation is high. LSR cannot do this — once it has cured, the scrap is scrap. On a high-volume programme the two effects compound, and together they are the whole margin.
• Medical grades exist. This surprises people. There are TPE formulations qualified for medical use — soft PVC replacement tubing for infusion sets being a familiar example.
• Processing. Because it re-melts, TPE suits certain high-speed forming processes.

But there is an important caveat on that second point: the higher the grade, the higher the price. Push TPE up toward medical or food-contact performance and its cost advantage starts to disappear — at which point you are paying near-silicone money for a material that still softens at 60 °C. Which material wins depends entirely on the application.

The difference underneath both: a physical change versus a chemical one

TPE and LSR are not two grades of the same thing. They are two different kinds of process, and that one fact explains most of the practical differences above — including why the temperature limits are what they are.

That last row is worth reading twice. The property that makes TPE economical — being able to melt and re-melt — is the same property that makes it soften in service. And the property that makes LSR expensive — a one-way curing reaction — is the same property that makes it dimensionally stable for years. Neither is a defect. They are two sides of the same coin, and which side you want depends entirely on what the product has to survive.

How each material is processed in practice

LSR: a two-component liquid, mixed 1:1

LSR arrives as a two-component material with the consistency of water. The two parts are mixed in a 1:1 ratio, and the functional additives go in during that mixing step — including the agents that set hardness and control cure time.

Colour is introduced the same way: pigments are dispersed into the mix so they become part of the material rather than sitting on top of it. We use environmentally-selected organic pigments for this.

TPE: pellets, melted and moulded

TPE is supplied as pellets and formed by melting and then cooling. Nothing is chemically transformed — the polymer that goes in is the polymer that comes out, which is precisely why the process is reversible and the scrap is reusable. Its properties come from the compound formulation rather than from a curing reaction, and that is also why its long-term dimensional stability is a different kind of question from silicone's.

Surface finish: a mould decision, not a material decision

This is the point most buyers get wrong. Whether a part comes out matte or glossy is not a property of the silicone or the TPE. It is decided by how the cavity of the mould is finished.

• Matte finish: the mould cavity is sandblasted and given an electroless nickel plating. The texture of the cavity is transferred to every part it produces.
• Glossy finish: a matte part can be converted to a glossy one through finishing work — spraying a transparent hand-feel coating over the surface.

The practical consequence: if you want a matte product, say so at tooling stage, because it is built into the mould. If you later decide you want gloss, that is a finishing step, not a new tool.

So which should you specify?

Frequently asked questions

How can I tell if a product is silicone or TPE?

Drop it in water. Silicone (LSR) has a density around 1.1 g/cm³ and sinks; TPE is around 0.9 g/cm³ and floats. Heat is the second check: TPE softens above roughly 60 °C, while LSR stays stable to around 200 °C. Smell is a supporting signal only, since modern TPE grades have had their odour substantially reduced.

Why is TPE cheaper than silicone?

Two effects that compound. First, the raw material: TPE pellets cost roughly two to three times less per kilogram than LSR. Second — and this is the part buyers often miss — TPE is a thermoplastic, so it can be melted and re-melted. Sprues and rejected parts go straight back into production, which means material utilisation is high. LSR cures through an irreversible chemical reaction, so once it has set, offcuts cannot be returned to raw material. On a high-volume programme the price gap and the utilisation gap multiply.

Is TPE food-safe or medical-grade?

Yes, it can be. Medical-grade TPE exists — soft tubing for infusion sets is a common example. The caveat is price: as TPE is pushed to higher grades, its cost advantage over silicone narrows and can disappear altogether. Whether it is the right choice depends on the application.

Does TPE look and feel like silicone?

Visually, often yes — which is exactly why photographs cannot settle the question. In the hand, LSR tends to feel drier and more silk-like, while TPE can be formulated to feel soft and skin-like. Surface finish is a separate matter entirely and is set by the mould, not the material.

Which material should I choose for an insertable product?

Look at the temperature spec first, then the lifetime. Anything that will be washed hot or must keep its shape and colour for years is an LSR application. TPE makes sense where the environment is mild, the volumes are high and the price point is tight.

Can a matte product be changed to a glossy one?

Yes — by spraying a transparent hand-feel coating on the finished part. Note that the matte/gloss decision itself is made at tooling stage: a matte surface comes from sandblasting plus electroless nickel plating of the mould cavity.