Injection Moulding Wall Thickness Guidelines: Design for Strength, Stability & Cost Efficiency

Wall thickness is one of the most influential variables in injection moulding design. It directly affects part strength, cooling time, dimensional stability, cosmetic quality, and ultimately the cost of production.

Components engineered with proper wall thickness are easier to manufacture, scale more predictably, and require fewer tooling adjustments — all of which reduce lifecycle cost.

For engineers and product designers, mastering this single design principle can prevent many of the defects that delay product launches.

Why Wall Thickness Matters

When molten plastic enters a mould, it must flow evenly and cool at a controlled rate. Variations in thickness disrupt this balance and introduce internal stress.

Consistent walls help achieve:

• Predictable material flow
• Even cooling
• Reduced warping
• Stronger structural performance
• Shorter cycle times

In many projects, improving wall design is the fastest route to lowering part cost.

Recommended Wall Thickness Ranges

Ideal thickness varies by polymer, but most injection moulded parts fall within a practical range.

• Small precision parts: 1.0 – 2.0 mm
• General commercial components: 1.5 – 3.0 mm
• Larger structural parts: 2.5 – 4.0 mm

Moving outside these ranges is sometimes necessary, but doing so requires careful engineering oversight.

The Hidden Risks of Thick Walls

It may seem logical that thicker plastic produces stronger parts — but excessive thickness often creates manufacturing problems.

Common Issues Include:

• Sink marks
• Internal voids
• Warping
• Longer cooling cycles
• Higher material consumption

These factors combine to increase production cost.

Why Thin Walls Are Not Always Better

Extremely thin sections can freeze before the mould fills completely, leading to short shots or weak structural performance.

Successful thin-wall moulding typically requires specialised tooling, higher injection pressures, and carefully selected materials.

Uniformity Is More Important Than Absolute Thickness

Maintaining consistent thickness throughout a part is often more important than chasing a specific measurement.

If transitions are unavoidable, keep them gradual. A transition ratio near 3:1 helps reduce stress concentrations.

Design Strategies That Improve Strength Without Adding Bulk

Use Ribs Instead of Thick Sections

Ribs provide stiffness while allowing the main wall to remain optimised for cooling.

Best practice: rib thickness should be roughly 50–60% of the adjoining wall.

Add Gussets for Structural Support

Gussets distribute load efficiently without dramatically increasing material usage.

Core Out Heavy Areas

Removing unnecessary mass promotes even shrink behaviour.

How Wall Thickness Impacts Production Cost

Wall design directly affects cycle time — one of the largest contributors to per-part pricing.

Thicker parts cool more slowly, keeping machines occupied longer and reducing hourly output.

Over large production runs, even small reductions in cycle time can generate substantial savings.

Collaborate Early With Your Injection Moulder

Manufacturing input during the design stage helps identify wall-related risks before tooling begins — when changes are still inexpensive.

This proactive approach often prevents the engineering revisions that inflate project budgets.