Shore A, Shore 00 and Shore C: How to Specify Silicone Softness Without Getting Burned

2026-10-12 · 9 min read · Materials · Silicone · Specifications · Sourcing

There is one sentence that causes more scrap, more rework and more quiet dissatisfaction in this industry than any other: "Make it soft."

"Soft" is not a specification. It is a description of a feeling, and two people in the same meeting will picture different things when they hear it. Worse, once you translate it into a number, there are three different gauges that number could be measured on — and the readings on them do not convert into each other. A supplier who quotes you "30" may mean something substantially softer or firmer than another supplier quoting "30" on a different scale.

This page is how to close that gap. It is written for buyers and product developers, so it stays on the specification side — what to write down, what to ask for, and how to confirm you got it.

Why "soft" costs money

Here is the pattern we see most often. A buyer sends the same brief to three factories: a shape, a size, a colour, and the word "soft". Three quotations come back. One is dramatically cheaper than the others, which looks like a win — until the samples arrive and the cheapest part is a firm, tacky, plastic-feeling product that the end consumer will describe as cheap.

What happened is not a price trick. The three factories interpreted "soft" three different ways, and the cheapest one made a firm part because firm material is faster to demould, produces less scrap and holds tighter tolerances. Nobody lied. The brief was simply not a specification.

Every one of those problems disappears once the softness is written as a number measured on a named gauge, with a tolerance. So the first thing to sort out is which gauge.

Three gauges, three different questions

Durometer readings come from pushing a shaped indentor into a material and measuring how far it travels against a spring. Different indentor geometry and different spring stiffness mean each scale is measuring a different range of resistance. Three scales matter in soft silicone work:

Shore A — the everyday rubber scale

The scale most people mean when they say "Shore" or "durometer". A blunt conical indentor, designed for cured rubber in the middle of the hardness range. It is the right gauge for firm parts and for the stiff sections of a product — bases, cores, handles — but it runs out of resolution at the soft end. A very soft silicone can read below the useful floor of the A scale, which is exactly when the reading stops meaning anything.

Shore 00 — the super-soft scale

Purpose-built for gels and very soft elastomers, with a larger hemispherical indentor and a much lighter spring. This is the scale for genuinely soft skin-like silicone, and it is the one we recommend naming in a specification whenever the product is meant to feel yielding or gel-like. Where the A scale bottoms out, the 00 scale is still reading comfortably.

Shore C — the scale that shows up in Chinese soft-silicone production

A third gauge that appears frequently in soft silicone supply in this region, and the source of a great deal of quiet confusion. It sits in the same territory as the soft end of the other scales, which is precisely what makes it dangerous: a Shore C number looks like a Shore A number, and means something different.

The point that matters most: readings do not convert

This is the single most useful thing on this page, so it gets its own section.

It is tempting to think of the three scales as three units of the same quantity — like centimetres and inches, where you can multiply by a constant and be done. They are not. They are three different measurements, taken with three differently shaped probes under three different spring loads. The relationship between them is not a formula. It is a set of empirical anchor points that only apply to the specific materials they were measured on.

We run our own cross-checks on production material, and the result is worth internalising. On the material we use, one reference point we have measured repeatedly is:

Read that carefully and notice what it destroys. A part reading 42 on the C scale is roughly equivalent to 18 on the A scale — not 42, and not a simple fraction of it. If you had assumed the two numbers were comparable, you would have ordered something more than twice as firm as you intended, and you would only find out when the samples arrived.

Two rules follow directly:

• Never convert between scales arithmetically. There is no coefficient that does this correctly, and any calculator that offers one is guessing.
• Always name the gauge, not just the number. "30" is not a specification. "Shore 00-30" is.

So what should your spec sheet actually say?

A hardness requirement that a factory can hit and you can verify has four parts, not one.

The fourth line is the one buyers leave out and then argue about. A durometer reading is a surface measurement, and the reading changes with the thickness of the part under the probe: press the same indentor onto a thin wall and onto a thick base of the same material, and you will get two different numbers. So "00-30" is only meaningful together with a statement of where on the product, and on what thickness, the number is taken.

Two practical notes on that:

• Specify finished-part measurement if what you care about is the product as sold. A cured plaque off the same batch can read differently from the finished, contoured part.
• Allow a real tolerance. A ±0 points specification is not achievable in production, and asking for it will get you either an argument or a part nobody can inspect.

Why the same number feels different from two suppliers

Once the gauge and the number are agreed, there is still a remaining reason samples can diverge, and it is worth understanding because it is not a trick either.

Hardness describes how the material resists a small local indentation. Hand-feel is a wider sensation, and it is assembled from several things hardness does not capture:

• Crosslink density and its uniformity. Two batches can land on the same gauge reading while feeling different — one springy, one dead — because the reading is a point sample of a bulk property.
• Additives and fillers. What was dispersed into the mix to reach that hardness changes how it behaves in the hand, even at an identical reading.
• Surface treatment. A translucent hand-feel coating makes a part glide where the same body would otherwise be tacky. That is a finishing decision laid over the material, not a hardness difference.
• Geometry. Wall thickness, internal voids and overall mass change how a part yields when squeezed. Two products reading 00-30 can feel quite different if one is 15 mm thick and the other is 30 mm.

The practical upshot: a hardness number narrows the field, but a physical sample closes it. That is not a reason to skip the number — it is a reason to get the number right and approve a part you have held in your hand.

How to verify softness without a lab

You do not need a durometer to make a good decision, and in fact we would argue against deciding from a number alone. What we do with customers who are choosing a softness is simpler and more reliable than any spec sheet:

1. Send a gradient, not a number. Instead of asking you to name a hardness, we cast the same shape in a small series of graduated hardnesses — typically five steps spanning the range that suits your product.
2. You squeeze them in order and pick. This takes a few minutes, and it settles a discussion that can otherwise run for weeks of emails. The samples are identical in shape, colour and surface, so the only variable is what you are feeling.
3. We then record that point and hold it. The chosen hardness is written into the record for that product, so the next order is produced at the same setting rather than at a fresh interpretation of the word "soft".

If you do want to measure, a handheld durometer of the correct type is an inexpensive instrument, but note the caveat from earlier: the gauge has to match the scale named in the spec. Measuring a soft gel part with a Shore A gauge — the one most people own — will produce a reading that is technically real and practically useless.

Why we write hardness into the product record

One last thing, because it explains a decision we made as a manufacturer rather than a piece of general advice.

Every product we make carries an internal code, and that code includes a hardness field alongside the mould, the colour and the finish. It is not decoration. It exists because the failure mode in this industry is rarely the first order — it is the third one, placed eight months later, when the person writing the email has changed and the phrase "same as last time" has to be interpreted by someone new. A recorded hardness setting turns that interpretation into a lookup.

If you are comparing suppliers, this is a fair question to ask: where does the agreed hardness live once the sample has been approved? A supplier who can point to a field in a product record will reproduce your part. A supplier who can only point to an email will reproduce something close, eventually.

Frequently asked questions

Is Shore 00 softer than Shore A?

Yes. Shore 00 is a different gauge, built for softer materials than the A scale resolves well. A material reading 00-30 is a genuinely soft, yielding silicone. The important point is not that one scale is "softer" than the other, but that a reading on one scale cannot be converted into a reading on the other.

Can I convert a Shore 00 reading into Shore A?

Not arithmetically. The two gauges use differently shaped indentors and different spring loads, so they measure different things. The relationship is a set of empirical anchor points on specific materials, not a formula. On our production material, for example, Shore C42 measures at approximately Shore A18 — a relationship worth knowing and not worth generalising. The safe practice is to specify on one named scale and stay on it.

What hardness should I specify for my product?

Choose the gauge first: Shore 00 if the product should feel yielding and skin-like, Shore A if it is a firm part or a structural section. Then do not guess the number — ask for a gradient sample set in your own shape and pick by hand. Softness interacts with wall thickness and overall geometry, so a number chosen from a table will often not be the number you actually want once it is in a product.

Why does the same Shore reading feel different from two suppliers?

Because hardness is one property and hand-feel is several. Crosslink density, additives and fillers, surface treatment, and the geometry of the part all contribute. Two parts can share a gauge reading and still differ in how they yield when squeezed. Use the number to narrow the field, and a physical sample to make the decision.

Should hardness be measured on a sample plaque or on the finished part?

On the finished part, if the specification is about the product you are selling. A durometer reading is a surface measurement and it varies with the thickness of material under the probe, so the same compound can read differently on a thin wall and on a thick base. State both the location and the part, and allow a realistic tolerance — ±5 points is typical.

Do you charge for hardness gradient samples?

Sampling on an existing mould is quick, because the mould already exists and only the mix changes. Tell us the shape and the approximate range you are aiming at, and we will quote the sample set with the rest of your enquiry — see the capabilities page for our standard sampling terms.