What Is a Bill of Materials (BOM) and Why It Matters to Your Contract Manufacturer

When you're preparing to engage a contract manufacturer, one of the most important documents you’ll share is your Bill of Materials (BOM). At first glance, it might seem like a simple list of parts, but to your contract manufacturer, it’s the main document they will use during the request for quotation (RFQ) process. 

An unclear or incomplete BOM can cause serious delays during the RFQ process. If critical details like material specifications, finishes, or quantities are missing, your contract manufacturer will need to follow up with questions, make assumptions that could lead to incorrect pricing or production errors. For example, listing just “aluminum” for a part might result in your contract manufacturer quoting 6061, when you actually needed 7075. That mismatch alone can derail the quoting timeline or lead to an unexpected outcome in production.

A clear and complete BOM will eliminate guesswork, improve communication, and speed up every step from quoting to shipment. In this post, we’ll explain what makes a good BOM, what your contract manufacturer needs to see, and how you can avoid common mistakes that slow things down.

Why a Good BOM Matters

To your contract manufacturer, the BOM is more than just a list of parts. Every detail in the BOM influences how your product will be priced, sourced, fabricated, and assembled. When the BOM is incomplete or vague, it immediately creates questions. 

An unclear BOM often leads to delays during the RFQ phase. Your contract manufacturer may need to ask follow-up questions, clarify assumptions, or even requote if critical information was missing in the original quotation. This back-and-forth can stretch a simple quote into a multi-week process. Worse, if assumptions are made without confirmation, such as choosing the wrong material grade, it can result in parts that don’t reflect the expected quality and a price point that does not match expectations. 

A complete BOM, on the other hand, streamlines everything. It enables your contract manufacturer to:

• Quote more quickly and accurately

• Order the correct raw materials or components

• Determine lead times and tooling requirements

• Flag any potential design or sourcing issues early

In short, the better your BOM, the smoother the process becomes for both sides. And while it might take a bit more effort upfront to document the right details, it pays off in faster quotes, fewer mistakes, and more productive collaboration.

What to Include in a Complete BOM

The BOM is one of the key components that your contract manufacturer needs to understand your product so they can offer an accurate quote. The more detail you provide, the less room there is for error or assumption.

Below is a breakdown of the key elements every BOM should include, along with why each one matters from your contract manufacturer’s perspective:

Part Number

Each item in your BOM should have a unique part number. This identifier helps both you and your contract manufacturer keep track of individual components, especially when updates or revisions are made. A part number eliminates confusion and ensures that everyone is talking about the same item, no matter how many variations or revisions exist.

Part Name

While the part number is the unique reference, the part name offers an additional layer of clarity. A simple descriptor like “Top Cover Plate” or “USB-C Connector” provides context and makes conversations about the BOM more intuitive for both teams.

Material

Listing a generic material like “aluminum” or “plastic” is not enough. Materials come in dozens of grades and formulations, each with different mechanical properties, costs, and manufacturing requirements. For example, aluminum 6061 is not the same as 7075, and the price, machinability, and strength are very different. Be specific to avoid incorrect assumptions.

Color

Color may seem subjective, but it doesn’t have to be. Instead of saying “blue” or “silver,” specify the exact color using a Pantone number. This is especially important for customer-facing products or brand-sensitive components where color consistency matters. For example, don’t just say greed, say Pantone 7733 C. 

Finish

Surface finish plays a critical role in both appearance and function. Whether it’s anodizing, powder coating, bead blasting, or electroplating, the finish affects the look, feel, and cost of the component. Your contract manufacturer needs this information to quote accurately and identify the correct process.

Quantity Per Assembly

Include how many of each part are needed to build one final product. For example, you might need multiple units of the same screw in a single assemble. The quantity will tell you how many unique parts are needed for the assembly. 

Thumbnail or Picture

Adding a simple image or thumbnail of the part goes a long way. It allows your contract manufacturer to instantly visualize the component and catch any mismatches between the name, material, or description. Visuals reduce ambiguity, especially when part names or descriptions are not intuitive.

Supplier or OEM Source

If the part is not custom-made and must be sourced from a specific brand or OEM (e.g., a particular switch, motor, or display module), list the manufacturer's name and their part number. This ensures consistency and prevents substitutes that could impact compatibility or performance.

Fabrication Method

If you know how a part should be made, such as CNC machined, injection molded, or die cast, include this in the BOM. This helps your contract manufacturer assess tooling requirements, lead times, and manufacturing feasibility. Even if your contract manufacturer proposes alternatives later, this gives them a strong starting point.

Link to Technical Drawing or 3D Model

One of the most valuable additions to a BOM is a link to the part’s 2D drawing or 3D CAD file. The CAD files are an important part of the RFQ process but when there is a link to the CAD file in the BOM, then this makes it more convenient for the contract manufacturer. 

Revision Level

If your product has undergone design updates, clearly indicate the current revision level for each part. This ensures that contract manufacturers are always working with the most up-to-date specs and helps prevent mix-ups between old and new versions.

Notes or Special Requirements

Use this field to flag anything unique about the part: regulatory requirements (e.g., RoHS compliance), packaging instructions, or assembly considerations. These notes can prevent surprises during production.

The more complete and unambiguous your BOM is, the easier it becomes for your contract manufacturer to support you, from quoting through to production. 

Why Detail Matters: Reducing Back-and-Forth

One of the most frustrating issues in the RFQ process is the endless back-and-forth caused by an incomplete BOM. When key details are missing from the BOM, your contract manufacturer is forced to either ask clarifying questions or make assumptions. Both slow things down and increase the risk of quoting errors.

Let’s say your BOM simply lists “plastic” as the material. That could mean ABS, PC, nylon, or dozens of other resins, each with different mechanical properties, costs, and moldability.

Even small gaps in information can delay your quote by days or even weeks. For example:

• Not listing a part quantity can lead to incorrect volume-based pricing.

• Missing part numbers can cause confusion between similar components.

• Omitting fabrication method may lead to quoting the wrong process (e.g., machining instead of molding).

Beyond delaying the quote, this lack of clarity can undermine your credibility. When a customer shares a disorganized or incomplete BOM, it signals to the contract manufacturer that the project may not be fully thought through. On the flip side, a clear and complete BOM shows professionalism, preparation, and respect for the contract manufacturer's time.

Ultimately, every detail you include saves time, improves accuracy, and speeds up your project. Investing in a strong BOM up front is far more efficient than answering a dozen follow-up questions later.

What to Do If You’re Not Sure What to Include

If you’ve never built a full BOM before, it’s completely normal to have questions. But don’t let uncertainty lead to delays or vague documentation. The best approach is to just ask your contract manufacturer what they need and aim to include as much clear, objective information as possible from the start.

Most contract manufacturers, including EPower Corp, are happy to review an early draft of your BOM and provide guidance on what’s missing or unclear. In fact, we prefer when customers over-communicate rather than leave critical details out. It’s much easier for us to trim down extra info than to chase down missing specifications.

Here are a few best practices if you’re still developing your BOM:

• Start with the basics: Part number, name, material, quantity, and process. Build from there.

• Flag unknowns: If you’re still deciding on a material or finish, leave a note instead of staying silent. This shows awareness and invites collaboration.

• Use placeholders with intent: For example, write “TBD – finalizing resin with CM” so the supplier knows to ask.

• Ask for a BOM template: Many CMs can provide a spreadsheet format or example that outlines what they expect.

• Aim for objectivity: Avoid vague descriptions like “blue” or “rough finish”—use color codes and specify finishes.

Providing a high-quality BOM is not about perfection, it’s about clarity, communication, and mutual understanding. The more information you offer up front, the faster and more accurately your supplier can respond.

Conclusion: BOM for Contract Manufacturer

Your BOM isn’t just an internal document, it’s one of the most important documents that are shared between the contract manufacturer and the customer. When done well, a BOM sets the tone for a productive supplier relationship. When it’s incomplete or unclear, it slows everything down and increases the risk of costly mistakes.

Think of the BOM as a tool that tells your supplier, Here’s exactly what we need, and now help us make it happen. The more objective and detailed it is, the faster your supplier can act, the more accurate your quote will be, and the fewer surprises you’ll encounter during production.

At EPower Corp, we view a well-prepared BOM as a sign of a thoughtful, professional team.If you're unsure how to structure your BOM or what to include, just ask. Reach out, we are happy to talk.