Flow length versus wall
A long thin path can freeze before the last tip fills. Mark the longest flow on a section view.
Thin wall design
Thin Wall Design for Injection Molding: Fill, Flow Length, and Rib Support
A thin skin needs resin, gate, vents, and ribs, not just a smaller wall callout. DFM review compares your nominal wall to flow length before steel is quoted.
Design guideline
Thin walls chase fill length, not a smaller caliper reading
Thin wall design is how a light skin fills, packs, and stays stiff. The work is flow length, resin, gate, vents, and ribs.
Thin sections save resin when the melt can reach the end of fill. As walls get thinner, pressure and shear rise. Gate location and vent paths matter more than on a chunky bracket. Ribs carry stiffness so you do not thicken the whole skin. NetProto does not publish a minimum wall. DFM review compares your nominal wall to flow length and rib support.
The wall thickness page picks the nominal skin. Uniform wall covers transitions. Flow length to wall owns the ratio question. Thin-wall molding owns press and mold. High-flow grades cover resin choice. The design guide hub lists every topic.
Roles
Which page answers which thin-wall question
Stay here for fill and support on a thin skin. Open a sibling for the nominal wall, the ratio, or the process.
| Page | Use it for |
|---|---|
| Thin wall design (this page) | Fill, resin, gates, and ribs once the wall is already thin |
| Wall thickness | Pick the nominal wall first |
| Uniform wall thickness | Gradual transitions, not a thin-to-thick step |
| Flow length to wall ratio | Distance versus skin. Not a NetProto table |
| Thin wall molding process | What the press and mold have to do |
| DFM review | CAD check of flow length and rib support |
Checks
What DFM review looks for on thin walls
Qualitative checks. NetProto does not publish a minimum wall thickness.
Resin and shear
Thinner skins raise pressure and shear. A high-flow grade can help. Geometry still dominates.
Ribs for stiffness
Do not thicken the whole skin to fix feel. Add ribs that reference the nominal wall.
Gate and last-to-fill
Place the gate so thin tips can fill, and give those tips a vent path.
Decision
A paper-thin skin versus a thin skin with support
Wrong: cut wall until it feels light. Right: keep a fillable skin, then add ribs, gate, and vents.
What goes wrong
- Short fills at the last rib tip or far edge
- Warp on a large flat thin region
- Hesitation lines on a cosmetic face
- A drawing that only lists a minimum wall and hides ribs and gates
What to try first
- Keep a fillable nominal wall, then add ribs for stiffness
- Place the gate so thin tips fill, with a vent at last-to-fill
- Call out resin family or a known high-flow grade
- Show the longest flow length on a section view
Drivers
What usually decides whether a thin wall fills
Qualitative drivers. This page does not publish a wall or ratio table.
| Driver | Why it matters |
|---|---|
| Flow length versus wall | Distance the melt must travel before it freezes. |
| Gate location | Sets which thin tip fills last and where weld or hesitation can sit. |
| High-flow resin grades | Help fill long thin paths. Still not a substitute for geometry. |
| Venting at last-to-fill | A sealed thin tip can short or burn even when the wall looks fillable. |
RFQ
Send these notes with CAD for a thin-wall review
The quote can start from CAD alone. These notes make the DFM pass specific.
Nominal wall and the thinnest section callout
Resin family or a known high-flow grade
Largest flow-length dimension on a section view
Rib plan for stiffness, if the skin must stay thin
Intended gate side, if you already have one
Cosmetic face that cannot accept hesitation or weld marks
Related
Related design guidelines
This page owns fill and support on a thin skin. Open a sibling for the nominal wall, the ratio, or the process.
Thin wall molding process
What the press and mold must do. This page stays on part geometry.
Thin wall molding processDFM review
How NetProto checks flow length, ribs, and gates on your CAD.
DFM reviewFAQ
Injection molding thin wall design FAQ
What is thin wall design in injection molding?
Thin wall design is how you keep a light skin filling, packing, and staying stiff once the nominal wall is already thin. The work is flow length, resin, gate, vents, and ribs, not a smaller caliper reading alone.
How thin can an injection molded wall be?
It depends on resin, flow length, gate, and cosmetic class. NetProto does not publish a minimum wall thickness. A high-flow grade can help, but geometry still dominates. Upload CAD so DFM review can comment on your section.
Why do thin walls short-shot or warp?
As the skin gets thinner, pressure and shear rise and the melt can freeze before the last tip fills. Large flat thin regions also warp. Ribs, a gate that reaches those tips, and a vent at last-to-fill reduce that risk.
How should ribs support a thin wall?
Stiffness comes from ribs and geometry, not from thickening the whole skin. Size ribs from the nominal wall so they do not create new thick islands. The rib page owns that feature. This page owns why the thin skin needs them.
Which resins fill thin walls most easily?
High-flow grades within a family help fill long thin paths. Geometry and gate still dominate. Put the family or known grade on the RFQ. The high-flow materials article covers grade choice. This page does not publish a resin list.
How is this page different from wall thickness or thin-wall molding?
Wall thickness picks the nominal skin. Uniform wall covers transitions. Flow-length ratio owns the distance-to-wall question. The thin-wall molding process page owns press and mold. This spoke owns fill and support once the wall is already thin. DFM review checks your CAD.
Next step
Upload CAD for DFM review of your thin walls
Share geometry, resin, flow length, and rib notes so review can check fill and support before steel is cut.