One change stands out in enquiries for silicone parts over the past two years: the silicone wall thickness on drawings keeps getting thinner. Where 1.5 mm was once normal, 0.5 mm, 0.3 mm and even 0.2 mm sealing lips or acoustic membranes now show up regularly.
The driver is not process showmanship (see cold runners and in-line inspection) but the product — wearables need to fit into smaller spaces, acoustic parts want thinner vibrating surfaces, and water-resistant designs would rather use one membrane than a whole structural part. Going thinner is not a smaller dimension; it is a different set of moulding conditions.
This note covers three things: what actually makes thin walls hard, what industry does about it, and which parts should not be thinned at all.
1. Three physical limits
- Fill resistance: halve the wall and flow resistance rises close to a square relationship. At the same injection pressure a thin cavity often cures before it fills, leaving short shots and flow marks.
- Venting: a thin cavity leaves little room for gas to escape. Trapped air raises local temperature and leaves burns — what looks like a small stain is often locally over-cured material.
- Demoulding and tearing: thin walls are weaker, so slightly uneven ejection deforms or tears them. Silicone is already modest in tear strength, and thin walls amplify that weakness.
Yield on thin-wall parts therefore depends less on the compound grade than on tool precision, mould temperature uniformity and venting.
2. Four routes that work
| Route | Solves | Cost |
|---|---|---|
| Cold runner with vacuum assist | Less premature cure in the runner; evacuates the cavity | Complex tooling, higher equipment cost |
| High mould temperature with short cycle | Lower viscosity, better fill | Demands uniform control; local overheating burns |
| Lower-viscosity grade | Flows further at the same pressure | Usually lower tear strength; needs structural support (material selection) |
| Micro-structured tooling | Etching, electroforming or precision milling for fine texture and micro holes | Higher tool cost; stricter maintenance and cleaning |
These routes are usually combined (equipment and process routes: capabilities). What decides whether the part can run at volume is mould temperature uniformity: a few degrees of difference between cavities and the short shot will always appear in the same cavity.
3. Five places where structure has to give first
- Wall transitions: dropping from 1.2 mm to 0.3 mm in one step concentrates stress; a step or ramp is safer;
- No sharp corners: in a thin wall every sharp corner is a tear initiation point, so the minimum radius follows wall thickness;
- Draft: thin parts rely on draft for release; ejector pins alone will not do it;
- Rib direction: ribs should run with the flow; a cross-flow rib becomes a dead zone;
- Leave a vent path: parting lines and insert gaps must vent — vacuum is not a substitute.
These are not design preferences; they are the conditions for making the part at all. Reviewing structure first is more useful than asking for a price first.
4. Inspection: geometry alone is not enough
- Wall distribution: section the part, measure multiple points on a vision system, and check the thinnest point against tolerance;
- 3D contour: laser scanning or CT for warp and deformation in thin regions;
- Optics and appearance: thin walls show uneven transmission and flow marks, so the appearance standard must state what is allowed;
- Function: frequency response for acoustic parts, leak rate and opening force for sealing lips (test capability).
Thin-wall parts often pass a dimensional report and still fail in use: deformation is invisible in the free state and appears once assembled against the mating part.
5. Five typical parts
- Acoustic membranes and diaphragms: thickness drives frequency response, and consistency matters more than the absolute value;
- Vent and sealing structures: membrane support rings and sealing lips that sit flush without adding volume;
- Wearable sensor patches: a thin silicone outer layer balancing skin comfort and conformity, commonly around 0.5 mm;
- Microfluidic and test consumables: micro channels and thin floors, the most demanding tooling work;
- Ultra-thin sealing lips: contact pressure comes from lip deflection, so thin and even is the precondition (see dimensional consistency).
6. Four cases where thin is wrong
- Areas that must resist tearing: a thin wall puts the weakest property in the most critical place;
- Long-term compression seals: too little material means too little compression reserve, and compression set appears sooner;
- Assembly load points: anywhere a clip or screw presses, a thin wall collapses;
- Low-volume projects: thin-wall tooling is expensive and rarely pays back over a few hundred parts.
7. Seven checks for design and purchasing
- What is the thinnest section, and does it sit in a stable moulding window?
- Is the transition from thin to thick a ramp or a step?
- Does the tool vent, and is vacuum assist used? How is parting-line accuracy held?
- What is the measured temperature difference between cavities?
- Does the appearance standard state limits for flow marks and transmission?
- Has the part been measured in the assembled state, not just free?
- Does annual volume amortise thin-wall tooling and a lower yield?
Conclusion
Ultra-thin walls and micro structures are among the more genuine advances in silicone moulding: they let wearables, acoustic parts and sealing structures fit into smaller spaces. But thin is not the goal — whether a thin wall runs reliably depends on tooling, venting and mould temperature, not on the compound grade.
Where a part must resist tearing, hold compression for years or take assembly load, making it thicker usually costs less overall. Reviewing structure before discussing process route is more effective than asking whether 0.2 mm is possible (tooling and sampling rules).
If you have thin-wall or micro-structured silicone parts, send the 3D drawing and duty conditions, and we will start with a structure and process feasibility check.