Knowledge · Materials guide
The short version: polyurethane is the workhorse for concrete, silicone earns its keep on fine detail and undercuts. The long version, with the reasoning, follows.
Start here
Anyone who tells you silicone is always better, or that polyurethane is always cheaper per pour, is oversimplifying. Both materials have earned their place on the bench, and the right one depends on what you're casting, how many, and how the tool is being handled.
This guide walks through the honest trade-off in the language of the yard, not the marketing brochure. If you finish it and you still can't tell which one your job needs, ring us and describe the panel.
Polyurethane
A wood-grain formliner running hundreds of pours on ordinary OPC precast. Polyurethane costs less per square metre, lasts longer under repeat handling, and doesn't need coddling. This is where polyurethane genuinely wins.
Formliners that get vacuum-lifted, hosed with cold water, stacked outside, walked on by mistake. Polyurethane takes abuse that would nick a silicone tool. If your yard is rough on tooling, spec polyurethane.
Where the customer has a tight budget and the relief doesn't need silicone's detail, polyurethane can save meaningful money on the tooling line. Not free — nothing decent is free — but noticeably less than silicone at the same size.
Board-marked concrete, sawn-timber texture, subtle stone facing. All shallow, no undercuts, no fine detail. Polyurethane holds these easily and outlasts silicone in the same application.
Silicone
A cladding panel with rope detail, foliage, deep-carved letters or crisp geometric edges. Silicone captures fine detail that polyurethane blurs. Every micron of the pattern reads on every panel.
Anything the mould has to flex past to release — cornices, deep coffers, three-dimensional bosses. Silicone flexes past undercuts that would jam a polyurethane tool or force you into a two-part mould you didn't want.
Rebuilding a lost cornice or finial from a surviving section. Silicone captures the weathering and tool marks that make the reproduction look right. Polyurethane loses those subtleties.
Some GRC face-mixes and some heavy pigment loadings degrade polyurethane faster than they degrade silicone. If your mix chemistry is unusual, silicone often survives longer despite costing more up front.
The trade-off
Polyurethane on straightforward relief. Lower cost per square metre, high pour count, low handling risk. Cost per pour is typically the lowest of any moulding route on this kind of work.
Silicone on the same relief. Higher cost per square metre, similar or slightly higher pour count, similar handling risk. Cost per pour is higher than polyurethane. If the relief doesn't demand silicone, this is where you're overspending.
Polyurethane on fine detail. Lower initial cost, but with a shorter usable life because fine details wear or blur faster in polyurethane than silicone. Cost per pour looks decent early, then rises as replacements come sooner.
Silicone on fine detail. Higher initial cost, longer usable life on fine detail. Cost per pour is often lower over a full programme than polyurethane on the same detailed job — the maths flips.
Honest bit
For a lot of jobs — moderate relief, moderate pour count, moderate handling — either material would give you a decent tool. In that case the deciding factor is usually the price you're comfortable paying up front, and whether the visual bar is really that low or you're being modest about your expectations.
If it's genuinely a coin flip, we default to polyurethane, because the total cost usually works out lower and the tool tolerates the yard better. But we'll say if we think silicone is quietly the better answer for a specific piece.
At a glance
How a two-part mould fits together
Swipe to see the whole diagram
FAQs
Yes. Silicone inserts set into a polyurethane surround are a very common solution. You get silicone detail where it matters and polyurethane elsewhere, saving cost.
No. On simple relief with lots of handling, polyurethane often outlasts silicone. Silicone's edge is on detail and undercuts, not on raw pour count.
Yes, if the pattern is preserved. We can pour a polyurethane tool, and if you decide later you need silicone for a subsequent run, cast that from the same pattern.
Silicone is more forgiving on complex geometry because it flexes past undercuts. On flat or gently curved pieces the difference is small.
Older formliner tradition used rubber compounds. They still exist, but for most modern applications silicone and polyurethane have overtaken them on cost, life and consistency.
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One photograph tells us what surface you're chasing, and one line about the mix tells us what silicone or polyurethane will survive it.
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