How to Select Food-Grade RTV for a Custom Mold

If you're selecting food-grade silicone for a custom mold, start with the food, the heat, and the market, then pick the RTV family. It isn't a Shore A, a color, or a drum label. For a cavity that will touch chocolate, batter, gummy syrup, or ice, it's a formulation plus a cure plus a finished-cavity result under a named rule: 21 CFR 177.2600 in the US, LFGB / BfR Recommendation XV under Regulation (EC) 1935/2004 in German files. Those programs don't nest. Platinum RTV is the usual dual-market skin after post-cure. Tin-cure RTV is the industrial and resin-casting start. A molded silicone *part* (spatula, consumer muffin cup) is a different quotation: HCR compression or LSR injection with a cold-runner.

Duty first, then chemistry

Put food type, contact time and temperature, market, split count, jacket, and recast plan on the RFQ. Chocolate is fatty. Gummy is often acidic and sugary. Ice is water at freeze. Butter cake is fat-at-heat. Name LSR or HCR only if you also want a molded *article* in parallel.

Tin-cure RTV: condensation, tin catalyst, byproduct leaving the network. Excellent for resin, wax, and many industrial jackets. Wrong default for dual-market bakeware.

Platinum RTV: addition-cure at or near room temperature. Vacuum-degas the A/B mix, pour against a finished master, then post-cure. Inhibition from dirty SLA masters, tin soaps, and sulfur is the process risk.

Shore A is how the cavity flexes, not a safety class. Soft ice and gummy tools (often 10A–30A) peel to release and still need a mother mold or they balloon. Aqueous 177.2600 is 20 then 1 mg/in² water reflux; fatty is 175 then 4 n-hexane. If the seller can't name flask, simulant, and cavity SKU, you haven't selected food-grade.

Common mix-up: platinum 20A as a food-grade spec

A lot of RFQs treat “platinum-cured 20A” as the food-grade callout. In the shop that usually means you've described chemistry and hardness and skipped the flask. Food-grade is a finished-cavity result on that color, after that post-cure.

What to ask when you're buying mold rubber

• What food, temperature, and market, and which method on *this* cavity?
• Is the specimen the production pour after post-cure and wash, or a cousin plaque?
• Platinum RTV or tin-cure, and why?
• Shore A plus jacket material — not Shore A as a safety class?
• Who owns the master, and is a recast included if pigment changes?
• Heat and dishwasher: what's actually tested for this grade?

Worked example: 12-cavity madeleine, US and Germany

A pastry brand wants a 12-cavity madeleine, 80 mm long, food-contact, dual-market, a few thousand dumps a month. Select platinum RTV, pigment frozen, jacketed two-piece, both 177.2600 and BfR XV on that cavity. Tin-cure is the wrong start. Molded spatulas, if they want them, are HCR or LSR on a separate line.

When this article is the wrong quote

If you're specifying a medical device, ISO 10993 / USP Class VI is a different file — don't use this page to skip a food flask, and don't use a food flask to skip a device file. If the mold only casts non-food resin, tin-cure against a master and jacket is usually enough; don't buy dual-market platinum paperwork by habit. Geometry can override quantity: a one-off platinum RTV chocolate tool can be the right spend even when a later LSR part program is on the roadmap.

Related reading: food-grade molds, why platinum RTV, safety standards, how to verify certifications.

What to send so we can select the rubber with you

• Food type, temperature, monthly dumps
• Market: US, DE/EU, or both
• Master type and who keeps it; one-piece vs keyed split
• Shore target, jacket, color freeze
• Named method: 177.2600 and/or LFGB/BfR XV on this SKU
• Any TDS plaque someone already attached (so we can reject cousins)

Send the food duty, the market, and a photo or STL of the master. We'll say platinum vs tin, jacket, and which flask belongs on the PO.

We would not recommend specifying platinum 20A as food-grade

We would not recommend treating Shore A as a safety class, or skipping the flask because the TDS says platinum. We would not pick tin-cure for a dual-market chocolate tool to save kit cost, and we would not borrow an LSR spatula plaque to qualify an RTV cavity.

Duty to chemistry:

flowchart TD
  F[Named food and market?] -->|missing| Q[Stop; write duty on RFQ]
  F -->|US and/or DE| C{Food touches the cavity?}
  C -->|resin only| T[Tin-cure RTV OK]
  C -->|chocolate bake gummy ice| P[Platinum RTV plus flask]
  P --> M{177.2600 and/or BfR XV?}
  M -->|cousin plaque| R[Retest this cavity and color]

Typical shop values: selecting the pour

| Item | Typical shop value | | --- | --- | | Platinum mix | 1:1 or 10:1 by grade | | Food-cavity Shore | 10A–20A with mother mold; ice/gummy often 10A–30A | | 177.2600 aqueous | 20 then 1 mg/in², water reflux | | 177.2600 fatty | 175 then 4 mg/in², n-hexane reflux | | Linear shrink | Platinum RTV ~0.1–0.3%; tin keeps moving in storage | | Post-cure | Ventilated; scale time to the thickest wall, not a 2 mm plaque |

Caption these as typical shop values, not a lab result on your SKU.

FAQ

Can I select food-grade mold rubber by asking for platinum-cured 20A? No. Platinum and 20A describe chemistry and hardness. Put food type, temperature, market, pour, color, jacket, and post-cure on the RFQ, then ask for that report.

Does a dual-market buyer only need the stricter of FDA and LFGB? No. The programs don't nest. Run both on the same cavity if both markets are in scope.

Is a medical ISO 10993 grade automatically selectable for chocolate molds? No. Chocolate molds are food-contact articles under 177.2600 and/or LFGB/BfR XV. Don't mix the paperwork to skip a flask.

What Shore A should I select for a muffin tray versus an ice-sphere tool? Pick from demold and slump. Ice tools often need more flex. Muffin trays need enough wall plus a jacket. Confirm food-contact on the hardness you'll ship.

If the TDS shows 230 °C, have I selected the heat rating? No. Heat limits are grade-specific. The TDS plaque isn't your muffin, gummy sheet, or ice tool. Write the duty on the drawing.