Part of TCI Group · UK design, UK manufacturing capability, since 2019
Platinum-cure silicone, tin-cure silicone, food-grade grades and polyurethane: what each one is genuinely good at, where each can fail, and why hardness is chosen around the cast rather than personal preference. Figures are indicative only and based on the supplier's data.
First principle
It is understandable that customers ask for the hardest mould available, assuming that harder means better made. It does not. A hard mould holds its shape, resists distortion under a heavy cast and lasts longer. However, it can refuse to release an undercut and make demoulding harder for anyone doing it all day.
A soft mould does the opposite. It peels off deep relief without tearing and is kinder to the operator. However, it sags under its own casting load, rounds off arrises over time and wears faster.
There is no single best grade. The right grade depends on your cast material, geometry, run length and the person on the bench, so finding it is a specification job. That is what this page is here to help with.
The families
Four material families cover almost everything that comes through our door. Each has jobs it is best suited to, and others it should not be used for.
This is the default choice for anything with detail, dimensional stability or a food declaration attached. It has very low shrinkage, a long working life as a tool, and can be post-cured. The trade-off is that it is fussy: sulphur clays, some resins, latex and certain tapes will inhibit the cure and leave a tacky face.
Cast moulds
More tolerant, forgiving and cheaper, it is a sensible choice for one-off work from an unknown pattern. It will cure against masters that would poison a platinum system. However, it shrinks more and ages more, so it is not the right route for food or precision work.
Hand-made moulds
You get a platinum system with the declarations that support its use against food, and PFAS-free where the grade allows. The paperwork is part of the specification, not an afterthought: we record the grade and batch against your order, so you can find the answer later.
Food-contact moulds
Compared with silicone, it is tougher, more abrasion-resistant and much stronger against tearing, which is why it is often used for concrete and cast stone work. It does not capture the finest relief as well, and you will need to take more care with release agents and moisture.
Polyurethane tooling
We select platinum systems for heat and thermal cycling, then post-cure them where the process needs it. Any rated temperature range we give you is the material supplier's figure, provided in writing, not our own claim.
High-temperature mouldsHead to head
The single most useful comparison in silicone mould making is also the one most often got wrong.
This covers the general behaviour of the two chemistries, rather than a quotation against a specific grade.
| Property | Platinum cure | Tin cure |
|---|---|---|
| Shrinkage on cure | Very low | Higher, and it continues slowly with age |
| Working life as a tool | Long, ages well | Shorter, stiffens and loses elasticity over time |
| Detail reproduction | Excellent | Good |
| Cure inhibition risk | Real. Sulphur clay, latex, some resins and tapes will stop it | Low. It cures against almost anything |
| Post-cure possible | Yes, where the grade allows | No |
| Food-contact grades available | Yes, with declarations | No |
| Cost of material | Higher | Lower |
| Best used for | Detail, repeat use, food work, dimensional stability | One-offs, unknown masters, awkward patterns, budget work |
If a master has been anywhere near sulphur-based modelling clay, please tell us before we cast. A test patch costs almost nothing, while a poisoned mould costs the whole tool.
Shore A
Shore A gives you one specific measurement, taken in one particular way: a sprung, shaped point is pressed into a sample of a given thickness, and the reading is based on how far it goes in. That is all it tells you.
A Shore A number alone won't tell you about tear strength, elongation, how well the material recovers its shape, how it behaves when hot, or how long the mould face will last. Two grades with the same Shore A number can behave completely differently on the same job, and routinely do.
We use the number as a starting point for the conversation, not as a specification on its own. When hardness genuinely matters, we confirm it using real parts made from the actual material. That's one reason prototype tooling exists.
We won't publish a grade-against-application table. Although it may look helpful, it is often wrong enough to cost somebody a tool.
Specifying
Answer these questions and the material choice is usually obvious. Leave them unanswered, and any grade is only a guess.
The material you choose - wax, plaster, resin, concrete, chocolate or silicone - affects release behaviour, chemical attack on the mould face and whether food declarations are needed at all.
Whether it's exotherming resin, an oven cycle, a heated line or an autoclave, heat is the fastest way to age a mould. Repeated cycling is harder on a tool than a single high peak.
Deep relief and undercuts mean lower hardness and greater wall thickness. A generous shape with proper draft can support a much harder, longer-lasting grade.
A maker carefully working at a bench needs different tools from a production operator at the end of a shift. We specify the mould around the person who will actually be demoulding it.
Food work
Food-contact work comes with a mould and a documentation job. The silicone grade must be declared food-contact silicone, and the declaration must be supplied against your order. We also record the batch used in your tool, so the information is still available if somebody audits you in three years.
PFAS-free grades are available, and where the material range allows it, these are the grades we specify for food work. If the grade you are asking about is not PFAS-free, we will tell you clearly rather than leave your question unanswered.
We are working towards BRCGS certification through the group's food division. The process is in progress and certification has not yet been awarded, so we will not describe it as anything else. For now, what exists is grade declarations, batch records and a specification against your order.
We handle food and confectionery moulding through the group's food division, so all the declarations for your job stay together in one place rather than being split across two companies.
Included
Your order records the material and specification. When you reorder, you receive the grade you approved, rather than whatever is nearest on the shelf.
Technical data sheets and declarations come directly from the material manufacturer. We pass on their figures as the manufacturer's own data, rather than presenting them as our own capability.
We keep the master so any replacement matches the tool you already have. That makes a like-for-like spare possible, rather than a fresh interpretation.
Honesty
We do not publish tolerance figures as a general capability. The accuracy you can achieve depends on the route, the geometry, the cast material, and the shrinkage of both the mould and the thing cast in it. A figure on a web page would describe another part, not yours. Buyers have been sold tooling on that basis before, so we prefer to discuss the requirements of your specific part.
We do not present a material supplier's temperature or hardness data as our own performance claim. If you need a rated figure, we will provide it in writing with the source attached, so you can hold the right party to it.
We do not hold ISO registration, and we do not claim to. BRCGS certification is being pursued through the group's food division, but has not yet been awarded. If you see anything from us suggesting otherwise, please tell us, as it is a mistake.
We do not run a materials laboratory. Instead, we specify materials from supplier data, test them on real parts where the job justifies it, and record what went in. For most mould work, that is the honest and sufficient approach. If your job needs formal material certification beyond a supplier declaration, please say so at enquiry stage, as this changes what we should quote.
If any of that means we're not the right fit for your job, it's better to establish that now, before a tool exists.
Related
Most specification conversations end up on one of these pages, giving you a useful place to start.
We explain how hardness is settled for the cast, the undercut and the operator, and why there is no published table.
Shore hardnessWe use declared food-grade platinum-cure grades that are PFAS-free where available, with declarations against the order.
Food-contact mouldsWe choose grades to suit your thermal cycle and post-cure them where the process needs it.
High-temperature mouldsChoose abrasive casts when tear strength and wear matter more to you than the finest detail.
Polyurethane toolingSorted by property
The same four pages, plus the two places where you would usually make a material decision.
This is where we work through wall thickness, draft and split line, as each one affects which grade will work for your part.
CAD and DFMHardness and release are settled on real parts in the real material before you commit to production tooling.
Prototype toolingFor surfaces where a single pinhole would mean rejection, we degas the material before it sets.
Vacuum castingEvery part inherits the master surface, so its material matters just as much as the mould's.
Master patternsOne group, four specialisms
One shared engineering team, one workshop and four specialisms bring the tooling knowledge behind a precast yard to a chandler through a single product.
Questions
This is almost always cure inhibition. Something the silicone touched has interfered with a platinum cure, such as sulphur-based modelling clay, latex, certain resins, some tapes or a few printed materials. The fix is to identify the culprit, then seal or replace the master. Test a patch before committing to the full pour. Tin cure will usually go off in areas where platinum will not.
No, it is a different mould. A harder mould holds its shape and lasts longer, but it will not release an undercut and is more difficult to demould. A softer mould releases deep relief more easily but wears faster. The right number is the one that suits your part, your cast and your operator.
Sometimes, but do not assume it will. Resin usually exotherms and attacks the mould face more aggressively than wax, so a tool sized for a wax life will not last as long with resin. Tell us both cast materials at enquiry stage, and we will specify the tool for the harsher one.
Yes, on request. We provide the manufacturer's documents, passing on their figures with the source attached rather than presenting them as our own performance claim.
For food work, we use food-grade platinum-cure grades (the food-safe kind). They are supplied with declarations and are PFAS-free where the range allows. Food safety comes from the specific grade and its declaration, not from silicone in general, so it needs to be specified rather than assumed.
It depends entirely on what you're casting. Against abrasive concrete and cast stone, polyurethane will usually outlast silicone comfortably. For fine detail work with a gentler cast, silicone will hold its surface for much longer. The cast material decides.
A small tear or lifted edge can sometimes be repaired. A degraded mould face cannot, because the surface is the product itself. If your tool is on a repeat programme, we prefer to hold a spare against the retained master rather than patch a worn face.
We will narrow it down together, then ask you to send us the part. Recommending a grade from a description alone can leave you with tooling that does not suit the cast, which is exactly what a material page like this is designed to help prevent.
Next step
The most cost-effective time to discuss materials is before the master is made and the production method is fixed. Once a tool exists, changing the grade is the hardest thing to do.
Send us the part, the cast material, the rough quantity and a note about the process it lives in. Ask the partnership team and you will receive a grade, the reason for it and the supplier data behind it.
At a glance
Silicone hardness in everyday terms
Swipe to see the whole diagram
Ready to start?
Send us a drawing, photograph or sample. We'll come back with a mould strategy, material recommendation and price.
Real people, a real workshop
No call centre and no middlemen. When you contact TCI Mouldings, you speak to the team who design, build and check your mould.
Thomas LaneManaging Director
George PrestonDesign & Project Manager
Kelly BallingerHead of Partnerships
Jim AndertonProduction Manager
TheodoreEmployee Welfare