Cost Drivers for Custom RTV Silicone Mold Quotations

If you're trying to price a custom RTV silicone mold, cost is a stack of master finishing, mixed rubber volume, split count, jacket work, and how many times you change the CAD after the first witness cast. It isn't a single number on a landing page, and this article doesn't invent one. Unmix the object before you compare money: a platinum RTV jacket around a printed master is one purchase. An aluminum two-plate HCR compression tool or a steel LSR tool with a cold-runner is a quotation for a molded silicone *part*, not for a cavity you pour into. If those three arrive in one spreadsheet titled "mold cost," the spreadsheet isn't comparable.

Master, rubber, and jacket as separate lines

You pay for master finishing (CNC, SLA/DLP post-cure, or work on a supplied sample), the mold box, the mixed platinum or tin RTV A/B, vacuum degassing, labor to pull the master, registration keys, any inner core, and a rigid support jacket. There's no cavity steel on this PO. Cost moves with physical size, number of mold pieces, and how ugly the master is. A dirty SLA master that inhibits platinum becomes a wasted pour, which is a cost even though no mill time was booked.

Coatings, unscrewing, and side actions are extras on metal part-tools. They aren't extras on a flexible RTV mold, which peels instead of actuating. Don't copy a plastic-injection or LIM tooling quote onto this job and call it done.

Cavity count is a volume bet, not a discount

One pocket costs less to pattern and more per dump. Sixteen pockets cost more master time, more rubber, and a jacket that has to stay flat, and they cost less per dump only if fill and peel stay even. There's no honest multiplier that says "8-cavity is 8 times the output at 1.2 times the tool." Unbalanced pockets on a gummy sheet ship the lightest cavity as the lot.

Family molds (two geometries on one sheet) look like a cost save. They're a save only if Shore A, shrink, and dump cycle can be the same. Mixing a shallow logo tile with a deep undercut mascot on one pour isn't a save. If the mascot is still changing, pay for one or two cavities.

Complexity that actually moves the quote

These features move shop time: undercuts that need splits or cores, molded-in logos with fine serifs, a mother mold in several pieces, a master that needs barrier coating against platinum inhibition, and walls of rubber that have to be thick enough to peel without tearing. A mascot with hair-like grooves isn't "the same as a rectangle plus 10%."

Color chips and carton marks move money less than buyers think. Food-contact is FDA 21 CFR 177.2600 or LFGB work on a grade, plus the finished-article rules of the market. Neither one is a texture. Each extra loop that changes CAD after the master is finished is a new pattern or a recast, not a free tweak. Don't ask a shop to "include UL 94 V-0 in the mold price"; UL 94 is a specimen class at a thickness.

Common mix-up: lining up an RTV jacket against an LSR steel bid

A lot of RFQs treat the cheaper number as the better mold. In the shop that usually means one bidder poured a sample and the other quoted a cold-runner for a silicone toy of the same outline. You can't tell until master / rubber / jacket / recast / sampling sit on separate lines.

What to ask when you're buying

• Can you break master, mixed rubber, jacket, keys/core, sampling, and recast into lines?
• Is this quote RTV mold-making, or HCR/LSR *parts*?
• Who owns the master and jacket after payment, and may the shop keep a copy?
• What quantity band and cavity count is the price built on?
• What's in the witness pack, and what does a CAD-driven recast cost later?

Worked example: 24-cavity bear sheet, about 5,000 dumps a month

A gummy brand wanted a 24-cavity bear on a 300 x 200 mm sheet, 18 mm pocket height, food-contact, about 5,000 dumps a month. Cost sat in a CNC or production-grade SLA master, keyed platinum RTV, a rigid jacket that stays flat on the depositor, and a recast term for the skin after wear. Comparing that number to an LSR cold-runner quote for a silicone toy of the same outline is how purchasing files two objects as one.

When a low RTV number is the wrong save

If you actually need thousands of molded silicone parts, the cheap RTV jacket isn't a discount; it's the wrong object and you'll still buy steel. If the CAD is open, extra cavities are extra recast area. Geometry can override quantity: a three-piece jacket with an inner core for a 45 mm hollow chocolate at 200 pours a month can cost more than a simple 12-cavity shallow tray at 4,000 dumps.

Related reading: how to cut development cost, lead time, what tooling means, custom RTV molds.

RFQ lines so two prices can be compared

Copy this. A number without these lines isn't a cost.

• Process: platinum or tin RTV mold (explicit ban on HCR/LSR substitution)
• Master type and who keeps it
• Cavity count vs dumps/month and first witness qty
• Split / keys / core / jacket material
• Shrink owner; food-contact path if any
• Recast of the skin: included or extra
• Witness pack contents

Send pocket STEP, dump material, monthly dumps, and whether you already have a master. We'll line-item master, rubber, jacket, and recast so the next PDF is the same object.

We would not recommend buying 16 cavities on an open CAD

We would not recommend lining an RTV jacket against an LSR cold-runner as if they were the same bid. We would not hide lab work inside mold cost.

RUUIPON Mold Structure Decision: price the split and the jacket as hardware. Geometry overrides quantity.

flowchart TD
  A[RFQ in] --> B{Object named RTV cavity?}
  B -->|no cold-runner| C[Reject as part-tool bid]
  B -->|yes| D[Line-item master rubber jacket recast]
  D --> E{CAD frozen?}
  E -->|no| F[One or two cavities only]
  E -->|yes| G[Cavity count vs dumps per month]

Typical shop values

Caption these as typical shop values, not a named lot.

| Item | Typical shop value | | --- | --- | | Mix | Platinum 1:1 or 10:1; vacuum degas | | Cavity Shore | 10A-20A with jacket | | Platinum shrink | About 0.1-0.3 percent | | Contrast LSR part shrink | About 2-3 percent on a different RFQ | | 24-cavity 18 mm bear sheet | About 5,000 dumps per month is a common band | | Outer-row vs 4.0 g | Edge often 3-6 percent heavy if sag is 0.5-1.5 mm |

FAQ

Why won't a serious shop put a mold price on the website? Because the object isn't defined. RTV jackets, aluminum HCR part tools, and steel LSR part tools don't share a number. A published "starting at" figure is either a poured sample or a bait quote.

Is a poured RTV mold always cheaper than a metal part tool? Usually, because there's no cavity steel. Size, split count, and a difficult master can still dominate. If you actually needed molded LSR or HCR *parts*, the cheap RTV number is the wrong object.

Does more cavities always lower dump cost enough to pay for the mold? Only if the pockets fill and peel alike, the jacket stays flat, and the quantity band is real. Extra cavities on an unstable drawing are extra recast cost.

Should compound and FDA or LFGB testing sit in the tooling quote? Keep them visible as separate lines. A mold can be simple while the grade and the lab work are not. Mixing them hides the recast versus the recipe.

How do I compare a China custom-mold quote with a local one? Line-item the same process (RTV), master type, cavity count, jacket, witness pack, and ownership. Ignore the cheaper number until those lines match.