Paper thin without ribs
- Short fills at the last rib tip
- Warp on large flat regions
- High sensitivity to lot variation
DFM
Thin Wall Design: Injection Molding Design Rules
Thin walls need resin, gate, and rib support, not just a smaller caliper reading.
DFM
Thin walls chase fill length, not bragging rights
Lightweight lids and housings need resin and gate strategy, not hope.
Thin sections reduce material and cycle time when the resin can reach the end of fill.
As walls get thinner, pressure and shear rise. Gate location and vent paths matter more than on chunky brackets.
NetProto DFM review compares your nominal wall to flow length and rib support before quoting steel.
DFM
Quote this rule with your CAD upload
NetProto DFM review flags these geometry patterns before steel is ordered.
- Call out draw direction and cosmetic faces on the model.
- Note resin family even when the grade is not final.
- Tighten tolerances only on mating features that need them.
Fill risk
Aggressive thin wall versus supported thin wall
Stiffness still comes from ribs and geometry, not from cheating wall thickness alone.
Thin primary wall plus ribs
- Ribs carry stiffness at controlled thickness ratio
- Gate placed to fill thin tips last with vent path
- Cosmetic face identified for weld line acceptance
CAD checklist
Send this with thin wall programs
Missing inputs delay qualified quotes.
Nominal wall and thinnest section callout
Resin family or known high flow grade
Largest flow length dimension on a section view
Cosmetic face that cannot accept hesitation lines
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
Design guide hub
All DFM topics on one route.
Design guide hubDFM article
Long form engineer guide.
DFM articleWall thickness
Baseline thickness rules.
Wall thicknessUniform wall
Transition thick to thin gradually.
Uniform wallRib design
Stiffness without extra wall thickness.
Rib designVisual reference
Molding context for this rule
Images from the Forge media library illustrate typical programs.
Injection molded part design review on CAD
Injection molded part design review on CAD
Plastic housing with ribs and bosses
Plastic housing with ribs and bosses
Engineer measuring molded component
Engineer measuring molded component
FAQ
Thin wall questions
Which resins fill thin walls easiest?
High flow grades within a family help, but geometry and gate still dominate. Upload CAD for program specific feedback.
Can I specify a minimum wall on the drawing only?
Yes, but also show ribs and bosses that affect fill balance.
Does thin wall always mean lower piece price?
Not if scrap, warp, or secondary straightening eat the savings.
Next step
Upload CAD for thin wall DFM
One hardened steel tool quote with piece price on the same program.