Gas Assisted vs. Conventional Injection Molding

Gas Assisted vs. Conventional Injection Molding: Which Is Right for Your Part?

Process Comparison · Gas Assist Injection · gasassistinjection.com

Conventional injection molding is the workhorse of plastics manufacturing. Gas-assisted injection molding (GAIM) is a specialized upgrade for parts with thick sections, strict weight targets, or sink-mark problems. This guide compares the two head-to-head so you can choose the right process for your part — and your budget.

Two processes, one result in mind

Conventional injection molding fills the cavity fully with plastic and packs it with pressure until the gate freezes. It is simple, well understood, and ideal for thin-wall and uniform-wall parts. Its limits show up on thick sections: sink marks, warpage, heavy weight, and long cooling times.

Gas-assisted injection molding (GAIM) injects nitrogen into the still-molten polymer after a partial fill. The gas creates a hollow channel in the thick section and keeps packing from the inside while the part cools. The result: lighter parts, fewer sink marks, and better dimensional stability on thick-wall geometry.

Head-to-head comparison

Where conventional molding is limited — thick sections, heavy parts, sink-prone geometry — GAIM changes the physics so those sections can be lighter and cleaner.

When gas-assisted is the better choice

GAIM earns its tooling cost when the part design gives it something to work with. Consider GAIM when you need to:

• Remove sink marks on thick bosses, ribs, hubs and handles.
• Cut weight — hollowing thick sections can remove 20–40% of part weight.
• Reduce warpage on long, slender or thick-wall parts.
• Shorten cycle time on thick parts by cooling a thinner effective wall.
• Lower holding pressure and reduce clamp-force requirements.
• Add stiffness with hollow ribs instead of heavy solid masses.

When conventional is the better choice

Conventional molding stays the right, lower-cost choice in many cases. Prefer it when:

• The part is thin-wall or uniform-wall with no thick, sink-prone sections.
• You need high clarity or optical surface quality where a hollow channel adds nothing.
• The geometry gives no stable path for the gas — gas would finger or blow through.
• Quantities are low and the extra gas-pin tooling cost cannot be recovered.
• The part is small, simple, and light already — GAIM offers no benefit.

Cost and cycle-time reality

The honest comparison is total part cost, not just tooling. Two factors matter:

• Tooling: GAIM molds cost a little more — gas pins, gas channels and sealing add to mold construction.
• Per-part cost: GAIM uses less material, shorter cycles and lower energy, so per-part cost usually falls at production volumes on suitable parts.

Bottom line: on thick-wall, sink-prone parts, the material and cycle savings typically outweigh the extra tooling cost once volumes are meaningful. On thin-wall parts, the extra tooling cost has nothing to pay for itself.

How to decide — a practical checklist

Run your part through these questions. Three or more “yes” answers point toward GAIM.

Bottom line

Conventional molding is the default — simple, proven, and right for thin-wall, uniform parts. Gas-assisted injection molding is the upgrade when thick sections, weight, or sink marks are the problem. Choose GAIM when the part has a stable thick section and you can recover the tooling cost; choose conventional everywhere else.

At Inyección de Asistencia de Gas, we design and manufacture molds for both processes in our own factory, so you get an unbiased recommendation — not one process pushed on you.