Wall Thickness for Jacketed Silicone Molds | RUUIPON

"Wall thickness" on a custom RTV mold is two numbers. The cavity skin is how much platinum rubber sits behind the dump face. Too thin, and you tear at logos and corners. Too thick on a glove with no jacket, and you still sag — you just sag with more gum in the pour. The jacket / mother mold is the rigid shell that holds a loaded sheet or a wet mass. If you specify one thickness for the whole tool, you will either over-pour rubber or skip the jacket and watch the outer row drop about 0.5–1.5 mm.

RUUIPON pours skin and jacket as separate lines in Bao'an since 2018. Prototype 3–7 business days after CAD lock. Production MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies. Tear at a thin logo island is a sibling failure (logo thin-wall tear); sag and curl sit with tray warpage.

Does not apply when wall thickness means the *dump* (a 2 mm chocolate shell, a hollow resin). That is cavity *depth*, not mold wall. It also does not apply to LSR/HCR *part* walls in steel; those drawings go to wydsilicone.com.

Cavity wall vs jacket wall

Cavity skin. Soft peel band 10A–20A on most gloves; 20A–30A when the skin is already thin and the jacket is doing the stiffness. Local islands at letters can be ~0.3 mm before we ask to thicken. A uniform 1–3 mm skin behind a simple cavity is a common shop start; we do not treat that as a measured lot. Corners and logo wells run thinner unless the master was designed with a back-fill.

Jacket. Plaster, resin, fiberglass, or a printed shell. Thickness here is "stiff enough for this wet mass and this span." A half-sheet gummy tray without a jacket prints outer-row grams 3–6% heavy when the edge sags 0.5–1.5 mm. Hardening the skin does not replace the jacket. See tear vs hardness.

Block molds. A thick RTV block with no jacket is a third family: lots of rubber, peel from a cube, used on some resin figurines. It is expensive in gum and still wants keys if you split. Do not order a block when what you needed was a 2 mm skin plus a mother mold.

flowchart TD
  A[Name the dump mass and the span] --> B{Loaded sheet or large wet pour?}
  B -->|Yes| C[Skin plus mother mold]
  B -->|No, small peelable dump| D{Thin islands or logos?}
  D -->|Yes| E[Thicken islands; keep a modest skin]
  D -->|No| F[Uniform skin, jacket optional]
  C --> G[Do not thicken skin to fake a jacket]
  E --> H[CAD lock]
  F --> H
  G --> H
  H --> I[3-7 day prototype — check sag and tear]

Typical shop values

Caption these as typical shop values.

Platinum shrink of 0.1–0.3% does not thicken a wall. ISO 3302-1 M2 is a drawing class, not a wall spec.

We would not recommend

We would not recommend pouring a 10 mm RTV skin to "make it stronger" on a half-sheet tray. Put that budget in a jacket. The extra gum sags too.

We would not recommend a 0.3 mm uniform skin on a whole figurine to save rubber. Islands at 0.3 mm are a letter conversation, not a whole-tool thickness.

We would not recommend matching wall thickness to the dump thickness ("2 mm chocolate so 2 mm silicone"). Unrelated numbers.

We would not recommend sanding the master to thin a wall after the first recast. You moved every later cavity. A tooling charge is not unrestricted ownership of that master.

Worked example (anonymized)

A 12-up pectin sheet, 4.0 g target, platinum 15A, no jacket, "3 mm wall" on the RFQ. First dump: center cavities ~4.0 g, outer row ~4.2–4.3 g (that 3–6% band), straightedge showed about 1 mm edge sag. Recast: same 15A, similar skin, rigid jacket. Grams evened. We did not thicken the rubber. CAD already locked; 3–7 day clock was a recast pour. $50 3D did not apply. MOQ 20 per design on the jacketed tool.

A second RFQ the same month: resin badge, 2 mm letters, 8 mm block, no jacket. Tear at the "A" crossbar. Recast with a modest skin, thicker island, thin jacket — less rubber, better life. Related reading: custom RTV molds.

The photo that would prove sag: straightedge across a loaded sheet, gap at the outer row, grams labeled on two cavities. A cut-section of a 10 mm block does not prove the tray was specified.

Common mix-up: one wall thickness on the PO as a quality grade

Purchasing writes "3 mm wall, food grade" and thinks they specified the tool. Food-contact is platinum plus a document path on the article (21 CFR 177.2600 extraction, LFGB separate). Wall is structure. You can have a 3 mm skin that sags, and a 1.5 mm skin in a jacket that holds grams. Ask for skin thickness *and* jacket yes/no as two lines.

What to ask when you're buying

• Cavity skin thickness vs jacket thickness — both on the PI?
• Loaded span: do we expect 0.5–1.5 mm sag without a jacket?
• Thinnest island (logo, corner) in millimetres?
• Block mold vs skin-plus-jacket — which family?
• Recast: is the unsanded master staying so we can change jacket without remodeling?

Related: tear vs hardness, tray warpage, contact.

Where thickness shows up in the quote stack

Rubber is priced by volume. A 10 mm block on a large tray is a different PI than a 2 mm skin plus a printed jacket, even if both say "custom mold, 20 pcs." Ask the quote to split master / 3D / rubber / jacket / recast. If the $50 CAD line is in play, it is for modeling the *cavity*, not for inventing a jacket thickness in email. Jacket span follows the dump mass you named.

If you freeze a too-thin skin into MOQ 20, you buy twenty tear-prone tools. If you freeze a thick skin and no jacket, you buy twenty sagging sheets. Thickness is a DFM mark before CAD lock, same as draft and split.

RFQ copy-pack — two wall numbers

Copy to [email protected]:

• Dump, piece weight or cavity volume, tray span
• Cavity skin: shop to propose / a millimetre target
• Jacket / mother mold: yes / no / shop to propose
• Logo file if islands may run ~0.3 mm
• Files in mm (STEP preferred)
• Simple 3D: USD $50 when that CAD scope applies
• Quantity: prototype after CAD lock, then MOQ 20 per design
• Recast custody of the unsanded master

Matched next step: send span, dump mass, and whether you want a jacket, not a single "3 mm wall" line. Phone +86 135 3006 2969. Licheng Technology Industry Park, Xinhe Blvd, Shajing, Baoan.

FAQ

Is a thicker silicone wall always a better mold? No. Thickness without a jacket still sags. Thickness on a hooked part still tears if the island is sharp. Jacket plus island design beat a 10 mm pour.

Can I skip the jacket if I order a 40A thick skin? We would not. Stiffness for a loaded sheet belongs in the jacket. A hard thick skin peels worse and still creeps on a long span.

Do you have a standard cavity wall in millimetres? We start in a 1–3 mm skin band for simple gloves and then thicken islands. There is no one factory standard that fits gummy sheets, resin busts, and concrete gloves. Name the dump.

Does platinum shrink change wall thickness enough to care? Typical 0.1–0.3% on the rubber is not how you grow a 0.3 mm island into a safe letter. Fix the island in CAD.

If the prototype sags, is the fix a new MOQ 20? The fix is usually a jacket on a recast prototype (3–7 days after any CAD change; if CAD did not change, it is a recast pour). Production remains MOQ 20 per design on the tool you approve. The $50 CAD fee applies only if we still need to model.