Injection Mold vs. Silicone Mold

The key difference between injection molds (steel or aluminum molds) and silicone molds is their intended use. Injection molds are made from metal and are designed for larger production runs, from a few thousand to millions of parts. Silicone molds are made from liquid silicone and are mainly used for rapid prototyping and small-batch production, typically around 20–25 parts per mold. The right choice depends largely on your project stage, production volume, budget, and material requirements.

What Is an Injection Mold?

An injection mold is a hard mold made from mold steel or aluminum. Processes such as CNC machining and Electrical Discharge Machining (EDM) are used to create the cavity and core inside the mold. The mold is then installed on an injection molding machine, where molten plastic is injected into the mold cavity under high pressure and temperature to form the final part.

What Is a Silicone Mold?

A silicone mold is a flexible mold made by pouring liquid silicone around a master prototype and allowing it to cure. It is commonly used with the vacuum casting process. PU (polyurethane) resin is poured into the silicone mold and cured at room temperature, so no high-temperature, high-pressure injection molding machine is required.

In simple terms:

Injection molding = hard mold + high-pressure injection

Silicone mold = soft mold + low-pressure casting

Injection Mold vs. Silicone Mold: 6 Key Differences

1. Different Manufacturing Processes

Silicone molds are made by pouring and curing liquid silicone around a master pattern. The process is relatively simple and does not require specialized injection molding equipment.

Injection molds, on the other hand, require precision metal machining, mold assembly, finishing, and injection molding trials. The overall manufacturing process is much more complex.

2. Different Lead Times

A silicone mold can often be completed in as little as 3 days, allowing the first vacuum-cast parts to be delivered quickly.

Injection molds generally take longer because the process includes mold design, CNC machining, EDM, assembly, polishing, and mold trials. An aluminum mold typically takes 2–3 weeks, while a steel mold usually takes 4 weeks or more. Complex molds may require additional time.

3. Different Cost Structures

A silicone mold is a relatively low-cost investment for prototyping and small-batch production.

An injection mold requires a higher upfront investment. However, the mold cost is spread across a much larger production volume. As the number of parts increases, the per-part cost can drop significantly.

This is why silicone molds are usually more economical for prototypes and very small batches, while injection molds become more cost-effective as production volume increases.

4. Different Mold Life

Silicone molds are considered consumable tooling. A typical silicone mold can produce around 20–25 parts, although the actual mold life depends on factors such as part geometry, mold complexity, undercuts, and draft angles.

After repeated casting cycles, the silicone can begin to lose its dimensional accuracy and surface quality.

Injection molds have a much longer service life. Aluminum molds can typically produce thousands to more than 10,000 parts, while properly designed and maintained steel molds can produce hundreds of thousands or even more than one million parts.

5. Different Material Performance

Vacuum casting with silicone molds typically uses PU (polyurethane) resin. The resin can be formulated to simulate the appearance and feel of plastics such as ABS or PP. However, its mechanical properties are not completely identical to those of the actual production material.

For example, properties such as crystallinity, impact strength, heat resistance, and long-term durability may differ from parts produced by injection molding with the final production-grade material.

With an injection mold, you can directly use the engineering plastic selected for mass production, such as ABS, PC, PA66, or POM. This allows the molded parts to have the same material properties as the final production parts.

6. Different Applications at Different Project Stages

Silicone molds are ideal for: concept validation, design and appearance evaluation, functional prototypes,small-batch testing, low-volume production, and typically around 10–50 parts.

Injection molds are better suited for: bridge or pilot production, production runs from hundreds to thousands of parts, product launch, and long-term mass production.

Comparison	Silicone Mold (Vacuum Casting)	Injection Mold (Steel/Aluminum)
Mold Material	Liquid silicone	Mold steel/aluminum
Manufacturing Process	Low-pressure casting with PU resin	High-temperature, high-pressure injection molding
Lead Time	3–7 days	Aluminum mold: 2–3 weeks; Steel mold: 4+ weeks
Mold Cost	Low	High — typically several to more than ten times the cost of a silicone mold
Typical Mold Life	Around 20–25 parts	Aluminum: thousands to 10,000+ parts; Steel: hundreds of thousands to 1 million+ parts
Material Similarity	Similar appearance and feel, but not identical to production-grade materials	Can use the same material selected for final production

How to Choose Between a Silicone Mold and an Injection Mold?

Injection mold vs. silicone mold: The right choice depends on the product development stage, production volume, budget, and material requirements.

The design is still being refined or may change: Choose a silicone mold. It offers a lower-cost way to test and validate the design before making production tooling.

The product design is finalized, and you need a small production run: Consider an aluminum injection mold. It provides a good balance between tooling cost, lead time, production volume, and material consistency.

The product is finalized, and you are preparing for mass production: Choose a steel injection mold. It offers long mold life, high durability, and stable part quality over large production volumes.

You need to perform drop tests, temperature tests, or other functional validation: Use injection-molded parts made from the actual production material whenever the test depends on real material properties. PU resin from vacuum casting cannot fully replace production-grade, injection-molded material for these tests.

FAQ

How many parts can a silicone mold produce?

A silicone mold can typically produce around 20–25 parts. The actual number depends on the part geometry, mold complexity, undercuts, draft angles, resin type, and casting process.

Are the materials used for silicone-molded prototypes the same as real plastic parts?

Not exactly.

Vacuum casting typically uses PU resin. It can be formulated to closely simulate materials such as ABS or PP in terms of appearance and feel, but its mechanical properties may differ from those of actual injection-molded parts.

Properties such as impact strength, heat resistance, crystallinity, and long-term durability may not be identical.

For small-batch production, should I choose a silicone mold or an aluminum mold?

For around 10–50 parts, a silicone mold is usually more economical and faster.

For hundreds to several thousand parts, an aluminum injection mold is often a better option because it offers better material consistency, longer mold life, and a lower cost per part at higher volumes.

From Prototype to Production with SG Prototype

SG Prototype provides a complete manufacturing solution from silicone molds and vacuum casting to aluminum and steel injection molds.

Injection mold vs. silicone mold: Whether you need a few functional prototypes, a small batch for market testing, or tooling for mass production, we can recommend the most suitable mold and manufacturing process based on your project stage, required quantity, material, budget, and lead time.

Have a new project in development? Contact us to discuss your prototype or injection molding requirements.