Shore 10A vs 30A for Complex Resin Molds | RUUIPON

For a complex resin part — undercut hair, hooked horns, a bail, a hollow bust — Shore 10A vs 30A is the second question. The first question is whether the silicone can peel off the dump without tearing, or whether you need a two-part, a removable plug, or a core. If you pick 30A because it "feels stronger," you often make the peel worse and tear the mold at the first aggressive demold.

RUUIPON uses a house call we name Mold Structure Decision before anyone mixes A/B on a resin tool. Bao'an shop since 2018. Platinum RTV, mix 1:1 or 10:1 by grade, vacuum degassed. Prototype 3–7 business days after CAD lock. Production MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies.

Does not apply when the resin part is a flat-back open tray (a coaster, a simple cabochon) with no hooks — then Shore is a peel-and-wall conversation, and the three-pour Shore chart is enough. It also does not apply to LSR *parts*; those drawings leave this site for wydsilicone.com.

Mold Structure Decision (do this before Shore)

Walk the part in this order. Do not skip to durometer.

1. Flat back? If yes, you can usually pour an open-back glove or tray. Shore then follows wall thickness and how hard you will flex.
2. If not flat: deep undercuts, and can the silicone peel safely? If the skin can stretch off the hook without a thin island tearing, a one-piece peel in a soft Shore (often 10A–20A) is still on the table.
3. If peel is not safe → two-part / removable plug / core. Keys, a defined parting, maybe an inner core for a hollow. Shore on the skin can stay soft; the jacket or mother mold takes the stiffness.
4. Large wet casting? Mother mold required, regardless of 10A or 30A. A floppy block prints a different cavity every pour.

flowchart TD
  A[Complex resin part] --> B{Flat back?}
  B -->|Yes| C[Open-back glove or tray]
  B -->|No| D{Deep undercuts — can silicone peel safely?}
  D -->|Yes| E[One-piece peel, soft skin 10A-20A]
  D -->|No| F[Two-part / plug / core]
  C --> G{Large wet casting?}
  E --> G
  F --> G
  G -->|Yes| H[Mother mold required]
  G -->|No| I[Jacket if the block is floppy]
  H --> J[Then pick cavity Shore]
  I --> J
  J --> K[CAD lock — 3-7 day prototype]

Shore enters at the box labeled "Then pick cavity Shore." 10A vs 30A is that box, not the whole flowchart.

What 10A and 30A actually do on resin

Around 10A–20A. The skin stretches. Mild undercuts release if the island of rubber is thick enough. Logos and hair still need a minimum feature conversation (often about 0.3 mm islands; we would rather thicken a serif than ship a stamp you throw away). Tear grade matters more than the durometer number. See tear vs hardness.

Around 20A–30A. Useful when the cavity wall is thin and a stiff jacket is already doing the work — you do not want a jelly wall collapsing while you peel. 30A is a poor first answer to "the last mold tore." Tearing at a hook usually means the structure was a one-piece when it needed a split, or the wall at the logo was too thin. Raising Shore makes that peel *less* forgiving.

Platinum shrink after a full cure is typically 0.1–0.3%. That band does not change because you picked 30A. ISO 3302-1 M2 is a drawing class for rubber articles, not a Shore picker.

Typical shop values

Caption these as typical shop values.

We would not recommend

We would not recommend answering a torn figurine mold with "make the next one 30A." Send a photo of the tear. If it is at a hook, we split or plug. If it is at a hairline serif, we thicken the island or add draft. Durometer is last.

We would not recommend a one-piece 10A glove on a part with a closed loop (a bail, a handle, a through-hole that traps rubber). Soft Shore does not invent a second demold direction.

We would not recommend skipping the jacket on a large wet PU pour because the skin is 30A. Wet mass still wants a mother mold.

Worked example (anonymized)

A 110 mm dragon bust, PU dump, horns that hook back toward the skull, 6-up. The RFQ said "Shore 30A, one piece, like a cake mold." Mold Structure Decision: not a flat back; peel around the horns was not safe (the horn root is a thin rubber island that would tear). We marked a keyed two-part through the horn plane, a 15A skin, and a rigid jacket. CAD lock after the buyer replied KEEP on the split screenshot. Prototype in the 3–7 business day window. First PU dump released at the horns. We never poured 30A. Production MOQ 20 per design. STL was already in millimetres, so the $50 3D line did not apply.

The photo that would prove the call: horn root on the failed one-piece, torn rubber still in the hook, vs the keyed split with the horn in the cope. We describe that shot; we are not inventing a factory-gate image.

Common mix-up: 30A is the "production" Shore and 10A is the "prototype" Shore

People borrow that language from metal tools (soft aluminum proto, hard steel production). RTV does not work that way. Production resin molds in this shop are often the same 10A–20A skin you prototyped, plus a jacket, plus a recast plan from the unsanded master. 30A is a wall-and-jacket choice, not a volume upgrade. A tooling charge is not unrestricted ownership of that master — say custody on the PO if you need the recast in your building.

What to ask when you're buying

• Flat back? If no, can this peel, or do we need a split / plug / core?
• Where will the rubber be thinnest on demold (horn root, bail, serif)?
• Cavity Shore vs jacket — specified separately?
• Dump system (PU / epoxy / UV) and peak °C?
• Who approves the KEEP / FLATTEN marks before CAD lock?

Related: epoxy resin molds, undercuts and split molds, DFM before tooling, contact.

RFQ copy-pack — 10A vs 30A after structure

Copy to [email protected]:

• Resin system and peak °C
• STL/STEP in mm, units stated; or sample
• Known undercuts, bails, through-holes, hollows
• Your preference: one-piece peel vs split vs "shop to propose from Mold Structure Decision"
• Cavity Shore if you still have a target after that call
• Jacket / mother mold: yes / no / shop to propose
• Quantity: prototype, then MOQ 20 per design
• Simple 3D: USD $50 only when that CAD scope applies

Matched next step: send the file with the undercut notes so we can mark KEEP or FLATTEN, not a Shore vote. Phone +86 135 3006 2969. Shajing, Baoan.

FAQ

If the part is complex, should I always order 10A? Order a structure call. 10A–20A is the usual *skin* for a peelable resin glove. If peel is unsafe, split first; the skin can stay soft. 10A does not save a closed loop.

When is 30A the right resin cavity? When a stiff jacket is already in the tool and the cavity wall would collapse in a softer gum. It is a thin-wall choice, not a "stronger mold" upgrade.

Can you just pour 10A over my hooked STL as a one-piece to see? We would not. A doomed one-piece wastes the prototype clock. We mark the split on the screenshot, you KEEP or FLATTEN, then CAD lock starts the 3–7 day pour.

Does raising Shore reduce platinum shrink? No. Platinum RTV after a full cure is still typically 0.1–0.3%. Shrink is a master-compensation topic, not a 10A vs 30A topic.

Will production molds be a different Shore than the prototype? Usually the same skin, same structure, jacket as specified. Volume is MOQ 20 per design and a recast plan, not a durometer bump. Tooling charge still is not unrestricted CAD or master ownership unless the PO says so.