Designing rubber parts for injection molding requires a careful balance of function, manufacturability, and material performance. Unlike rigid plastics, rubber behaves differently under heat and pressure, so understanding the key design principles can save time, reduce scrap, and result in higher-quality parts.

Here are some essential tips to keep in mind when designing rubber components:

1. Optimize Wall Thickness

Consistent wall thickness is critical. Thick sections can lead to uneven curing, shrinkage, or internal stresses, while extremely thin sections may tear or fail during molding. Aim for uniform walls wherever possible and avoid sudden changes in thickness.

2. Include Proper Draft Angles

Draft angles are slight tapers that allow the part to release from the mold easily. Even rubber parts benefit from 1–3° draft angles in the right places, particularly on complex or deep features. This reduces the risk of tearing or deforming during ejection.

3. Consider Flow and Venting

Rubber flows differently than plastic. Avoid overly long thin features, and design gates and runners (or let your manufacturer suggest them) so the material fills the mold evenly. Proper venting is essential to allow air to escape and prevent voids or pinholes.

4. Minimize Undercuts

Undercuts complicate the mold design and may require side actions or collapsible cores. While some undercuts are unavoidable, try to design features that can be molded in one piece to simplify production and reduce costs.

5. Material Selection Matters

Different rubber compounds behave differently during molding. Consider the material’s shrink rate, hardness (durometer), and chemical resistance when designing features. Collaborating with your manufacturer early helps ensure the design aligns with the material properties.

6. Allow for Tolerances and Post-Curing

Rubber parts often experience slight dimensional changes after molding and curing. Designing with tolerances in mind ensures your part fits as intended. Discussing post-curing processes with your manufacturer can further improve stability and performance.

Partnering with Primo Rubber Co.

At Primo Rubber Co., we combine decades of experience with advanced injection molding techniques to help you turn designs into durable, high-quality rubber components. Our team can review your CAD files, suggest design improvements, and recommend materials that optimize manufacturability and performance.

Whether it’s seals, gaskets, or custom molded components, Primo Rubber Co. is your trusted partner in creating rubber parts that meet your exact specifications — the first time and every time. Contact Primo Rubber Co. today to learn more about our custom rubber molding capabilities and material options.