DFM GUIDE — DESIGN FOR MANUFACTURABILITY

Wall Thickness Guide
for Silicone & Rubber Molding

Wall thickness is the single most impactful design parameter in elastomer molding. Getting it wrong causes voids, warpage, and rejected parts.

What Is Wall Thickness?

Wall thickness determines how uniformly the material cures, how much it shrinks, and whether the mold fills completely. In silicone and rubber molding, the material is a thermal insulator — meaning thick sections cure slower at the core than at the surface.

This creates a fundamental tension: thick enough to fill and structurally sound, thin enough to cure uniformly and avoid defects. The recommendations below are based on thousands of production parts across HTV, LSR, and rubber compression processes.

Recommended Wall Thickness by Process

Process	Min (mm)	Recommended (mm)	Max (mm)	Risk if Exceeded
Compression Molding (HTV)	0.5	1.5 – 6	12	Internal voids, uneven cure
LSR Injection Molding	0.3	0.5 – 3	5	Air traps, incomplete fill
Rubber Compression	0.8	2 – 10	20	Porosity, long cure time
Extrusion (Wall)	0.5	1 – 5	10	Ovality, cooling warp

Why Wall Thickness Matters

Curing Uniformity

Silicone is a thermal insulator. Thick sections cure slower at the core — causing over-cure at the surface (brittleness) and under-cure in the core (mechanical failure).

Shrinkage & Warpage

Thick and thin sections shrink at different rates (silicone: 1.5–4%). Non-uniform walls = internal stress = dimensional warpage after demolding.

Mold Fill & Flow

In LSR injection, very thick sections trap air. In compression molding, thick preforms take longer to flow to extremities — risking short shots and voids.

Design Guidelines

Maintain uniform wall thickness throughout the part. Variations >2:1 (thick:thin) cause uneven cure.
If thickness must change, use a gradual taper (minimum 15° transition angle).
Avoid thick solid sections >10mm (compression) or >5mm (LSR). Consider coring out or using ribs instead.
Rib thickness should be 60–80% of nominal wall to avoid sink marks.
Use generous fillets (min 0.5mm radius) at wall intersections — improves flow and reduces stress concentration.
LSR thin walls: Can fill as thin as 0.3mm, but ejector pin placement becomes critical to avoid deformation.

Common Defects from Wall Thickness Errors

When wall thickness is not controlled, the following defects appear in production. Each defect has a specific root cause and a specific fix — but prevention through correct DFM is always cheaper than correction.

The image shows a comparison of good parts (uniform wall, clean surface) versus defective parts (voids, warpage, blistering). These defects are not random — they are predictable consequences of specific design choices.

Common Defects from Wall Thickness Errors

Defect	Root Cause	Solution
Internal Voids	Thick section, trapped air/volatiles	Reduce wall thickness, add venting, vacuum molding
Warpage	Non-uniform shrinkage	Uniform wall thickness, symmetrical design
Short Shot (LSR)	Thin wall + air trap	Optimize gating, increase injection pressure, add vents
Surface Blistering	Over-cure surface / under-cure core	Reduce cure temp, improve preform accuracy
Excess Flash	Oversized preform in thick sections	Optimize preform weight, improve mold precision