Silicone Mold Tolerance and Shrinkage

A soft silicone mold does not have one universal tolerance or shrinkage value.

Dimensional outcome can depend on:

• CAD/master accuracy
• master-production process
• silicone formulation
• cure
• mold support
• measurement condition
• casting process
• environmental condition

The correct approach is to define critical-to-quality dimensions and validate them under a repeatable condition.

Mark:

• fit dimensions
• sealing dimensions
• cavity weight/volume
• equipment pitch
• cosmetic-only dimensions
• reference dimensions

Not every dimension needs the same tolerance.

Soft parts/molds change shape under handling.

Define:

• supported or free state
• fixture
• temperature if important
• measurement tool
• datum/reference

Final accuracy cannot be better than the master/tool/process chain.

Confirm material-specific shrink against the supplier’s technical data and the approved prototype; there is no single shrink table for every formulation.

Use:

• selected material data
• prototype measurements
• project-specific compensation

For gummy/chocolate/wax:

• dimensional tolerance may matter less than actual piece weight/volume
• validate the real formula/process

If a prototype consistently measures off-target:

• identify source
• update CAD/master
• revalidate
• then release production

For fit-sensitive lids, gaskets or assemblies:

• define mating part
• physical sample
• gap/compression
• functional acceptance

Can you hold ±0.1 mm on every silicone mold?

Do not assume that. Define the specific feature and measurement condition.

Can you measure directly from the real polyresin/plastic sample?

Yes, and that can be valuable for fit-critical projects.

Can shrinkage be compensated in CAD?

Sometimes, after the actual process/material behavior is understood.

Is platinum silicone shrinkage always 0.1–0.3%?

No.

Should every dimension be inspected?

Focus on agreed CTQs.