Category: Mold Manufacturing Reading time: 6 min Meta description: Hot runner vs cold runner injection molds — compare cost, cycle time, scrap rate, maintenance, and when to choose each. A practical comparison for mold buyers. URL: /blog/hot-runner-vs-cold-runner/ Tags: hot-runner, cold-runner, injection-molding, mold-design, runner-system
The runner system — the channels that deliver molten plastic from the injection machine nozzle to the cavity gates — is one of the most consequential design decisions in injection molding.
Choose cold runner and you pay for less upfront but generate more waste. Choose hot runner and you reduce waste and cycle time, but increase mold complexity and maintenance cost.
This guide compares both systems so you can choose what fits your production.
Cold runner: The molten plastic fills the runner channels, then cools and solidifies along with the part. When the mold opens, the runner is ejected as a solid piece — and either discarded or reground.
Hot runner: The runner channels are kept at melt temperature by heated manifolds. Only the part solidifies — the runner stays molten for the next cycle. No scrap is generated.
| Factor | Cold Runner | Hot Runner |
|---|---|---|
| Mold cost | Lower ($2,000-8,000 less) | Higher (+$3,000-15,000) |
| Material waste | 5-50% (regrind possible) | 0% (no runner waste) |
| Cycle time | Longer (cool runner before eject) | Shorter (no runner cooling) |
| Automation potential | Manual or robot de-gating | Automatic de-gating at mold |
| Gate mark | Visible, may need trimming | Minimal or none |
| Color change time | Quick (purging small channels) | Slow (manifold must be purged) |
| Maintenance | Low (simple system) | Higher (heater, thermocouple, seal) |
| Suitable plastics | All plastics | Most (except high-temp or corrosive) |
| Cavity pressure | Higher loss through cold channels | Lower loss (direct fill) |
| Mold complexity | Simple | Complex |
| Cold Runner | Hot Runner | |
|---|---|---|
| Mold cost | $12,000 | $18,000 |
| Runner weight (per part) | 15g (15% waste) | 0g |
| Cycle time | 28 seconds | 22 seconds |
| Per-part cost (qty 100,000) | $0.68 | $0.52 |
| Total cost including mold | $80,000 | $70,000 |
The break-even point for a hot runner is typically 50,000-200,000 parts depending on part size, runner weight, and material cost.
| Issue | Cold Runner | Hot Runner |
|---|---|---|
| Common failures | None (mechanical) | Heater burnout, thermocouple failure, seal leakage |
| Preventive maintenance | Minimal — polish gates every 100K cycles | Replace heaters/seals every 500K-1M cycles |
| Repair cost | $100-500 (polish/clean) | $500-3,000 (heater/seal replacement) |
| Special skills needed | No | Yes — trained hot runner technician |
| Downtime per failure | 1-2 hours | 4-8 hours |
A compromise for specific applications: the runner is designed with larger channels. The outer layer of plastic solidifies and insulates the molten core, allowing the center to stay melted for the next shot. This reduces waste without adding heaters.
Only suitable for: Small molds, specific materials (PP, PE), short production runs.
| Your Situation | Recommended System |
|---|---|
| Production < 50,000 parts/year | Cold runner (lower mold cost) |
| Production > 100,000 parts/year | Hot runner (material savings + automation) |
| Engineering plastic (expensive) | Hot runner (0% waste matters) |
| Color changes every run | Cold runner (fast purging) |
| Cosmetic part, no gate mark | Hot runner (valve gate preferred) |
| Heat-sensitive plastic | Cold runner (thermal degradation risk) |
| Multi-cavity (> 8 cavities) | Hot runner (balanced fill is easier) |
| Low budget for mold | Cold runner (lower upfront investment) |
If you decide on a hot runner, these are the specifications to specify:
| Parameter | Standard | Premium |
|---|---|---|
| Manifold type | Single-level | Multi-level for complex gating |
| Nozzle type | Open or valve gate | Valve gate with hydraulic/pneumatic actuation |
| Heating system | Standard coil heaters | High-performance cartridge heaters |
| Temperature control | ±5°C | ±1°C (closed-loop) |
| Seal technology | Standard tip seals | High-temperature seals with backup rings |
| Brand | YUDO, HASCO | Mold-Masters, Synventive, INCOE |
Tell us your production volume and part requirements on app.moldkey.com/quote and we'll recommend the optimal runner system for your mold.