HERS Material Type in SAP: A Practical Perspective

You’ve probably heard the saying, “Garbage in, garbage out.” Nowhere is this truer than in the world of master data. SAP is a powerful enterprise system, especially when it comes to managing supply chains, maintenance, and procurement. But even the best software can’t help if your data fundamentals aren’t strong.

One area often overlooked in SAP implementations is the HERS material type. In conversations with many customers, I’ve noticed that this concept often takes a backseat—perhaps because earlier SAP setups were built with a legacy mindset that didn’t fully anticipate the evolving need for data governance and traceability.

Let’s break it down.

ERSA vs HERS: What’s the Difference?

In SAP, ERSA is your organization’s internal identifier for spare parts—think of it as your own catalog number. It doesn’t matter who manufactures the part or where you source it from; if it serves the same function, it gets the same ERSA code.

On the other hand, HERS is a special material type meant for managing Manufacturer Part Numbers (MPNs). If you need to maintain multiple part numbers for a single material, the HERS material type can be used to create Manufacturer Part Number (MPN) materials, allowing different part number information to be managed under a single material.

This is useful when you want to control the exact source or quality of materials. You can specify to the vendor which manufacturer should supply the material and the corresponding part number used by that manufacturer.

It’s also useful when you receive identical parts from different manufacturers and need to track them separately—either for regulatory reasons or internal quality control.

Let’s say you’re managing a spare part—like an industrial bearing—that your company uses across various plants. Internally, you track it as an ERSA material in SAP, but here’s the catch: you source this part from multiple manufacturers. Each supplier has its own Manufacturer Part Number (MPN), but the part performs the same function. Instead of creating separate material numbers for each version, you use the HERS material type to manage these manufacturer-specific parts. These HERS materials don’t carry inventory or valuation—they just act as references linked to your ERSA part through MPN mapping. Now, when it’s time to place a purchase order, you simply reference the ERSA material. SAP automatically checks the source list and quota arrangements—maybe 70% of your supply comes from BOSCH and 30% from SKF—and routes the order accordingly. Purchase Info Records (PIRs) ensure the right pricing and delivery terms are applied for each MPN. Meanwhile, your inventory remains clean and consistent, tracked only against the ERSA material. This setup helps you keep procurement flexible, ensure regulatory traceability, and avoid the chaos of constantly updating your BOM every time a vendor or part number changes.

• Use Case – When you want to manage materials by manufacturer’s part numbers and link them to your own internal part (Usually ERSA and ROH).
• Inventory – HERS materials cannot be stocked or purchased directly. They are non-valuated and serve as a reference only.
• Procurement – MPN materials can be used in procurement processes along with internal material number
• During procurement, the manufacturer’s part can be used for evaluation or compliance purposes, but inventory, MRP and valuations are managed on the internal part.

When Should You Use HERS?

HERS isn’t just an optional add-on—it’s invaluable when:

• You want to maintain multiple Manufacturer Part Numbers (MPNs) for single internal material
• You need to standardize procurement but allow vendor-specific flexibility
• You receive functionally identical parts from different manufacturers.
• You need to meet compliance or traceability requirements.
• Your procurement strategy is built around MPNs and substitution logic.

It’s important to note: HERS materials are non-valuated. That means they can’t be purchased or stocked directly. Instead, they act as reference points, while actual inventory is tracked against the internal ERSA material.

Key Relationships of MPN

1. MPN with Source List and Quota Arrangement

The Manufacturer Part Number (MPN) in SAP integrates with the Source List and Quota Arrangement to control which manufacturer’s part (via HERS) is procured and from which vendor, ensuring quality, compliance, and sourcing flexibility.

In a source list: (Transaction ME01)

• You specify allowed vendor + MPN combinations.

• Can define:

• • Valid periods
  • Fixed sources (to enforce vendor selection)

In a Quota Arrangement (Transaction MEQ1)

• You define how vendors split quantities for each MPN or internal material.
• Allows weighted procurement decisions, e.g., 70% Bosch, 30% SKF, as in the example below

Procurement will reference MPN and route POs to the correct vendor + manufacturer based on source list and quota.

The key benefits with this relationship is

• Ensures manufacturer compliance in regulated industries.
• Supports vendor diversity with control.
• Avoids incorrect substitutions by enforcing MPN-source linkages.

2. MPN with Purchase Info Records (PIR)

In SAP, MPN (Manufacturer Part Number) integrates with Purchase Info Records (PIR) to allow manufacturer-specific procurement. This is essential when the same material can be sourced from different vendors and manufacturers, each with their own conditions.

The MPN based PIR creation (Transaction ME11) allows to

• Create a PIR for Material (ERSA) with MPN (HERS)
• In PIR , you specify manufacturer, part number , pricing , delivery and lead time
• A checkbox that this PIR is MPN relevant – which is used during PO creation to filter PIR’s by MPN preference.

The benefits of using MPN with PIR’s are:

• Enables price comparison by manufacturer and vendor.
• Supports manufacturer control while maintaining procurement flexibility.
• Useful for regulated industries needing traceability.

3. MPN and Bill of Materials

This relationship is one single advantage of maintaining HERS to help with all the data challenges when part numbers are changed. It allows

• Consistency – A single internal material number (ERSA) is referenced in BOMs, but that material can map to multiple MPNs behind the scenes.
• Flexibility – Helps in maintaining flexibility in sourcing without changing the BOM frequently.
• Part Number Changes – There is often many reasons, where part numbers are changed for the same part. It allows to not to change the actual bill of material.

Below is an example of a use case:

• You have a resistor in a BOM.
• Internally, it is managed as a single material number.
• It can be sourced from multiple suppliers (each with a different MPN).
• SAP maps MPNs to this internal material and uses source list/quota arrangement or info records to determine the best supplier during procurement — without changing the BOM.

Prospecta’s Master Data Solution—MDO allows the rigour and relationships of all the above components to be combined and provides an easy user interface for maintaining and governing MRO master data.

Some examples below on how MDO One View of  iMRO brings them together.

In Conclusion

Good data isn’t just about clean spreadsheets—it’s about systematic, future-ready practices. That means avoiding workarounds like stuffing MPNs into ERSA descriptions and instead embracing the robust capabilities SAP offers with HERS.

If you want to take it further, tools like Prospecta’s MDO simplify and streamline these complex relationships. From internal parts to manufacturer tracking, MDO OneView for iMRO brings it all together with an intuitive interface and strong data governance.