Plastic Injection Mold Cavity: Choosing Between Single and Multi-Cavity Tools

When planning for plastic injection molding, a time will come when you need to decide to inest into a single-cavity a multi-cavity tool. This choice has a major impact on your tooling investment, production cost, lead times, and scalability.

The number of cavities in your mold determines how many parts you can produce with each shot or cycle. A single-cavity mold creates one part per cycle, while a multi-cavity mold produces multiple identical parts at once. The more cavities you add, the higher the upfront tooling investment, but the lower your per-unit cost becomes over time.

So how do you decide which direction is right for your product? In this article, we’ll break down what an injection mold cavity is, compare the pros and cons of single- and multi-cavity molds, and help you determine the best fit based on your production volume and long-term goals.

What Is an Injection Mold Cavity?

In plastic injection molding, the cavity is the empty space within a mold where molten plastic is injected and formed into the desired shape. Each cavity produces one part per molding cycle. A mold can have a single cavity or multiple cavities, depending on how many parts you want to produce simultaneously.

A standard injection mold is made up of two main halves:

• The core side (usually the moving side)

• The cavity side (usually the stationary side)

The total number of cavities in a mold has a direct impact on both production speed and cost. A single-cavity mold produces one part at a time. A multi-cavity mold can produce two, four, eight, or even more parts in a single cycle. The more cavities you have will increase output, but also require more expensive tooling.

Single-Cavity Molds

A single-cavity mold produces one part per injection cycle. It’s the most straightforward type of injection mold and is often used during the early stages of product development or when production volumes are expected to be low. Because there is only one cavity, the tooling making process is simpler, which results in a lower cost. 

For startups, prototyping stages, or niche products with modest annual demand, single-cavity molds offer a practical entry point. They provide the flexibility to test product-market fit, validate the design in real-world use cases, and make design changes with minimal additional tooling investment. If you expect revisions or have not finalized the product design, starting with a single-cavity mold can save time and money.

However, the tradeoff with single-cavity molds is in production efficiency. Because only one part is made at a time, the cycle time per unit is higher. This impacts your per-part cost when scaling up. As volume increases, the cost of labor, machine time, and overhead gets spread across fewer units, resulting in a higher cost per part compared to a multi-cavity solution.

Here’s a quick breakdown of typical pros and cons:

Advantages of Single-Cavity Molds:

• Lower upfront tooling cost

• Easier and cheaper to modify for design changes

• Simpler mold design and faster lead time

• Ideal for prototyping or low-volume production

Disadvantages of Single-Cavity Molds:

• Higher unit price at scale

• Slower overall output

• Not suitable for high-volume or fast-growing products

If your annual volume is under a few thousand units or you’re still finalizing the design, a single-cavity mold is often the most cost-effective and flexible path forward. But once you’re confident in the design and expect demand to grow, transitioning to a multi-cavity setup may offer better long-term savings. 

Multi-Cavity Molds

A multi-cavity mold is designed to produce multiple identical parts in a single injection cycle. Instead of one cavity, these molds include two, four, eight, or even more cavities arranged within the mold base. The primary goal of a multi-cavity mold is to maximize output and reduce the cost per unit. 

From a production standpoint, the benefits are significant. If a single-cavity mold yields 1 part per cycle, a 4-cavity mold produces 4. That means within a similar cycle time, you’re generating 4 times the output. This has a direct impact on the efficiency of your production line and the unit economics of your product. While the initial tooling investment is higher, the payoff comes in the form of dramatically lower per-part costs when amortized over a high volume of units.

Multi-cavity molds are most suitable for established products with stable designs and predictable demand. They make the most sense when you know you’ll be producing tens or hundreds of thousands of units per year and are focused on cost reduction and quicker lead times. 

However, there are trade-offs to consider. Multi-cavity molds take longer to machine and use more steel than a single-cavity tool. Also, if you decide to modify the design, it will be more expensive to modify the entire tool. You might need to remake the tool. 

Here are a few key points to summarize the advantages and limitations:

Advantages of Multi-Cavity Molds:

• Lower cost per unit at high volumes

• Higher output per hour = faster delivery

• Better suited for scaling up and high-volume runs

Disadvantages of Multi-Cavity Molds:

• Higher upfront tooling cost

• Longer lead time to build

• More complex maintenance and potential for unbalanced filling

Less flexibility once design is locked in

A multi-cavity mold should be treated as a long-term investment. If your product is already validated in the market and you’re looking to scale efficiently, this tooling strategy can drastically improve your margins and throughput. But if your design is still evolving or your demand forecast is uncertain, it might be better to start with a single-cavity mold and scale up later.

When to Choose Single vs. Multi-Injection Mold Cavity

Choosing between a single-cavity and multi-cavity injection mold isn’t solely about upfront investment, it’s a strategic decision that affects your lead times, scalability, and per-unit cost. To make the right choice, you’ll need to evaluate your production goals, budget, demand forecast, and product lifecycle stage.

Choose a Single-Cavity When

A single-cavity mold is the right choice when flexibility, lower initial investment, or design iteration is more important than high output. This is especially true during the early stages of a product’s life cycle, when you're still learning about your market or refining the design.

Consider a single-cavity mold if:

• Your annual production volume is low (typically under 10,000 units)

• You’re in the prototyping or validation phase

• You anticipate multiple design changes or iterations

• You want to reduce upfront tooling investment

• You’re launching a product with uncertain demand

For early-stage startups, pilot runs, or low-volume SKUs, starting with a single-cavity mold gives you the flexibility to learn and pivot without committing too much capital. If demand picks up, you can always upgrade to a multi-cavity version later.

Choose a Multi-Cavity When

A multi-cavity mold becomes the smarter choice when you’ve validated your product, understand your market demand, and need to scale production efficiently. The upfront cost is higher, but the payoff comes through reduced per-unit costs and faster output.

Choose a multi-cavity mold if:

• You have consistent, high-volume production needs (10,000+ units/year)

• Your product design is finalized and unlikely to change

• You're aiming to lower unit costs to improve margins or stay competitive

• Speed and production efficiency are critical to meet customer demand

• You have the budget to invest in higher tooling costs upfront

Multi-cavity molds are a long-term investment for stable, growing products. They help optimize your supply chain by minimizing labor, machine hours, and production time per part.

Conclusion: Injection Mold Cavity

Choosing between a single-cavity and multi-cavity injection mold comes down to a careful balance of cost, flexibility, and production goals. A single-cavity mold offers lower upfront investment and greater adaptability, making it ideal for prototyping, early-stage products, or low-volume production. A multi-cavity mold, on the other hand, is a long-term solution for high-volume runs, delivering significant savings on per-unit cost and greater production efficiency once your design is locked and demand is clear.

Neither option is universally better, it depends on where you are in your product journey. The right decision should be informed by your expected volumes, product lifecycle, tolerance for design changes, and available tooling budget.

At EPower Corp, we work closely with our customers to evaluate their needs and recommend the most appropriate mold cavity strategy. Whether you’re launching a new product or scaling up production, our team helps ensure your tooling investment aligns with your business goals.

Need help deciding which mold type is right for your product? Contact us today to discuss your injection molding plans.