What Custom RTV Silicone Molds Are in Shop Language

If you're writing "custom silicone mold" on an RFQ, the shop still has to know whether the silicone is the cavity or the article. On this site the silicone is the cavity: platinum- or tin-cure RTV poured against a master, pulled, and used to cast chocolate, gummies, resin, wax, or a short industrial run. A steel HCR compression tool or an LSR injection tool with a cold-runner is a different quotation for a molded silicone *part*, and it won't dump pectin.

Custom, in that RTV sense, means the pocket didn't exist as a catalog tray. You still pick platinum or tin, a Shore A from a real grade, a split scheme, and whether a rigid support jacket ships with the block. The word custom doesn't invent a process for you.

Custom versus a stock tray

Stock molds exist for ice cubes, generic bakeware, and common gummy animals. They're custom only in color or a pad-printed carton mark. The moment the pocket shape, cavity count, logo depth, or durometer is yours, you're buying a poured tool even if the outer frame looks like last year's sheet.

Overlay the catalog pocket on your CAD. If the lip and the undercut already match, you're shopping color. If the mascot, the letter with negative draft, or the registered sheet size is yours, the RFQ is for a custom RTV cavity, and the shop still needs a master, a mold box, and a plan for keys.

China-origin capacity for poured food and craft molds is large. That doesn't turn a trading-company showroom of trays into a mold-making bench. Ask about vacuum degas, master finishing, and platinum-versus-tin control before you ask about the city.

Common mix-up: the CAD is the candy, the title says "mold"

A lot of RFQs treat a STEP of the finished bar or gasket as the mold. In the shop that usually means we guess whether you want a flexible cavity whose pocket matches the article, a metal tool that produces a silicone article, or both in sequence. Those are separate purchase orders. Mixing them is how you receive a pretty poured block when you needed 5,000 compression gaskets, or a quote full of heaters when you needed a chocolate tray.

A poured platinum RTV block and an LSR injection tool can share a Shore A number and share almost nothing else. Shrink bands differ, flash logic differs, and food-contact paths differ. A COC that says "silicone mold, 50A" without naming RTV, the master, and the jacket isn't a specification.

Tin-cure RTV is a third chemistry inside the same object. It's often cheaper and more inhibition-tolerant on dirty masters, and it keeps shrinking in storage. Don't mix tin mold-life folklore with LSR tool life; the LSR tool is metal and isn't this product.

What to ask when you're buying

Send these before you compare prices:

• Is this quote for a poured RTV cavity I'll cast into, or for a molded silicone *part*?
• Who makes and who keeps the master after the job, and may the shop keep a copy?
• One-piece glove, keyed split, inner core, and is there a rigid jacket / mother mold?
• Platinum or tin, which Shore A grade, and which food-contact path if I need one (21 CFR 177.2600 extraction, and/or LFGB / BfR XV)?
• What's the cavity count against my dumps-per-month band, and is a recast of the skin in the price?

If the quote only says "custom silicone mold" and a number, you're not comparing the same job.

Worked example: 8-cavity bar, about 500 pours a month

A confectionery line wanted an 8-cavity bar, 120 x 60 x 12 mm, food-contact, about 500 pours a month, with a recessed brand 0.4 mm deep in the pocket. The RTV job was a CNC (or fully post-cured SLA) master, a registered two-piece platinum cavity, and a resin or fiberglass jacket so Shore 10A-20A rubber wouldn't balloon under chocolate. A recast of the face after a logo change is usually cheaper than a new master, provided the jacket still keys.

A parallel PDF quoted heated steel, cold-runners, and valve gates. That's a molded silicone *part*. It doesn't ship as a tray you pour into. Both documents said mold cost; only one was this product.

When this article is the wrong quote

If you need thousands of vulcanized silicone *parts* (gaskets, baby-care, keypad webs), don't buy an RTV cavity and hope it becomes a press tool. Quote HCR compression or LSR injection with a cold-runner on a parts OEM. A catalog ice sheet that already matches the cube is also the wrong spend for custom. Geometry can override quantity: a one-off, deep-undercut resin figurine is still a custom RTV job even at 20 pieces, while 10,000 identical silicone spatulas are not.

Related reading: what tooling means on an RTV PO, how we make the mold, custom RTV molds, food-grade molds.

What to send so the quote is for this object

Copy this list. A price without these lines isn't comparable.

• Object: poured platinum or tin RTV cavity (not HCR, not LSR part tool)
• Master: CNC, SLA/DLP, or physical sample; who keeps it
• Pocket STEP or sample photos; 2D with fill-weight or logo depth if those matter
• Hardware: one-piece / keyed split / inner core / jacket material
• Casting material and working temperature
• Cavity count, first lot, monthly dumps or pours
• Food-contact path if needed: 21 CFR 177.2600 and/or LFGB / BfR XV
• Recast of the RTV skin: included or extra

Send the pocket STEP (or sample photos), the material you'll cast, and whether you need a split. We'll name platinum vs tin, jacket, and whether a recast belongs in the price.

We would not recommend mixing three objects on one line

We would not recommend sending one RFQ that says "custom silicone mold" and accepting whichever PDF comes back cheapest. We would not raise Shore A first to "make it custom." We would not cut LSR steel "so we can scale later" while you still need a cavity to dump pectin or chocolate into.

RUUIPON Mold Structure Decision: flat back? open-back RTV. Else deep undercuts the rubber can peel? stay one-piece. If it cannot peel, two-part / plug / inner core. Large wet casting or Shore 10A-20A? mother mold / support jacket.

flowchart TD
  A[What are you buying?] --> B{Silicone is the cavity?}
  B -->|yes, pocket is catalog| C[Stock tray]
  B -->|yes, pocket is yours| D[Custom RTV: master box keys jacket]
  B -->|no, silicone is the article| E[Different RFQ: HCR or LSR part tool]
  D --> F{Bail / negative-draft letter / two-sided logo?}
  F -->|yes| G[Keyed split or core]
  F -->|no, shallow| H[One-piece glove]
  D --> I{Soft 10A-20A or wet pour?}
  I -->|yes| J[Mother mold required]
  I -->|tiny shallow| H

Typical shop values

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

| Item | Typical shop value | | --- | --- | | Cavity Shore | 10A-20A platinum RTV skin, rigid jacket behind it | | Mix | Platinum 1:1 or 10:1 by grade; vacuum degas until the foam collapses | | Linear shrink of platinum RTV | About 0.1-0.3% after full cure; tin keeps moving in storage | | Contrast: HCR / LSR *part* shrink | HCR about 1.5-2.5%; LSR about 2-3% — different RFQ | | 8-cavity 120 x 60 x 12 mm bar | About 500 pours/month is a common first food-mold band |

FAQ

Is a custom silicone mold the same thing as a custom silicone part? Usually not. Here the mold is the flexible RTV cavity you cast into. A custom silicone part is an article that leaves a metal HCR or LSR tool, which is a different RFQ and a different factory cell.

Can one custom tool run as both an RTV tray and an LSR part tool? Not as a drop-in. The RTV job is master, box, pour, and jacket. The LSR job is heated steel or aluminum with gates and, often, a cold-runner. A shop can sometimes use the same CAD for both, but that's two tools and two shrink policies.

Does "custom" mean I must buy a unique compound? No. Most custom RTV programs run catalog platinum or tin grades. Custom is the cavity. Unique colors, extra post-cure of a master, or a listed FDA/LFGB file are choices on top of that cavity.

When is a stock silicone mold enough? When the pocket shape, cavity count, and durometer already exist and you only need color or a printed carton mark. The moment the geometry is yours, you're in custom RTV tooling even if the outer sheet looks familiar.

What's the fastest way to get a quote I can't use? Send a photo titled "silicone mold" with no process, no Shore A family, and no statement of whether the silicone is the tool or the part. The numbers that come back won't be the same object.