What wall thickness is usual in injection molding?

Most injection molded products have a wall thickness between 1.5 and 3 mm, depending on material and flow path. More important than the exact number is uniformity: thick zones cool slower and cause sink marks and shrinkage cavities, while zones that are too thin may not fill completely.

Why isn’t a thicker wall stronger?

Bending stiffness scales with the third power of the construction height, not with wall thickness itself. You get stiffness from shape (ribs, crowning, turned edges), not from mass. A thicker wall costs quadratically more cooling time and is more prone to sink.

What does uneven wall thickness cost in practice?

Uneven wall thickness results in sink marks, shrink cavities, and warping, and extends the cycle time because the thickest zone determines the cooling time. Keep the thickness difference within 25 percent of the nominal wall, with a gradual transition across at least 3x the difference.

Design for Manufacturing / Wall Thickness

DfM deep dive

Wall thickness: the most important choice in any injection molding design

The wall thickness determines filling behavior, shrinkage, cycle time, weight, part price and quality simultaneously. Injection molding is a process of thin, uniform walls; virtually every other design rule is derived from this. An injection molded product cools from the outside in. Thick zones cool more slowly, continue shrinking for longer, and pull the product out of shape or cause sink marks on the surface.

Therefore, aim for a single nominal wall thickness throughout the entire product and solve stiffness with shape (ribs, doming, edge profiles), not with mass. Stiffness comes from geometry, not thickness.

Uniform wall thickness lesson plate: equal wall thickness prevents sink marks and long cooling time

Indicative wall thickness ranges per material

Material	Common range	Note
PP	0.8 to 3.5 mm	Flows excellently, can be locally thinner (film hinge)
ABS	1.2 to 3.5 mm	All-rounder, predictably good
PC	1.0 to 3.8 mm	Tough but viscous, thin long flow paths are difficult
PA6 (unfilled)	0.8 to 3.0 mm	Thin works well, watch moisture absorption after molding
PA6 GF30	1.0 to 3.0 mm	Anisotropic shrinkage, warpage risk with uneven walls
POM	0.8 to 3.0 mm	High, predictable shrinkage; thick zones cause shrinkage cavities

Indicative for standard grades; the achievable thickness depends on flow path, grade and mold setup.

Transitions between wall thicknesses

Sometimes a thickness difference is unavoidable, for example at a functional surface or a connection to an insert. Make the transition gradual: keep the difference within 25 percent of the nominal wall and let the transition run over a length of at least three times the thickness difference. Let the melt flow from thick to thin, not the other way around.

Eliminate any solid zone without mechanical function with a core-out: a recess from the non-visible side that brings the zone back to nominal wall thickness. This makes a solid button into a thin-walled tube, a thick foot into a ribbed shell.

Wall thickness works together with ribs, corners and draft: see the full DfM pillar or go directly to ribs and stiffeners.

What does this mean for your design?

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