Hubs is now Protolabs Network. Find out more

Get instant quote

What’s the best SPI surface finish for your injection molded part?

What SPI surface finishes does Protolabs Network have for injection molding custom parts? Check out the standard SPI mold finishes we offer and our material recommendations to get the most out of injection molding.

Injection Molding SPI surface finishes

What are the SPI surface finishes available through Protolabs Network?

This table contains all of the SPI injection molding surface finishes we offer.

Finish SPI* standard Finishing Method Typical surface roughness Ra (μm)
Super High Glossy finish A-1 Grade #3, 6000 Grit Diamond Buff 0.012 to 0.025
High Glossy finish A-2 Grade #6, 3000 Grit Diamond Buff 0.025 to 0.05
Normal Glossy finish A-3 Grade #15, 1200 Grit Diamond Buff 0.05 to 0.10
Fine Semi-glossy finish B-1 600 Grit Paper 0.05 to 0.10
Medium Semi-glossy finish B-2 400 Grit Paper 0.10 to 0.15
Normal Semi-glossy finish B-3 320 Grit Paper 0.28 to 0.32
Fine Matte finish C-1 600 Grit Stone 0.35 to 0.40
Medium Matte finish C-2 400 Grit Stone 0.45 to 0.55
Normal Matte finish C-3 320 Grit Stone 0.63 to 0.70
Satin Textured finish D-1 Dry Blast Glass Bead #11 0.80 to 1.00
Dull Textured finish D-2 Dry Blast #240 Oxide 1.00 to 2.80
Rough Textured finish D-3 Dry Blast #24 Oxide 3.20 to 18.0
As machined - Finished to the machinist’s discretion 3.20 (with visible machining marks)
  • SPI (Plastics Industry Trade Association) standards
Manufacture smarter

To get started with injection molding or get a quick refresher before manufacturing your custom parts, check out our comprehensive guide to injection molding.

SPI surface finishes for injection molding
Protolabs Network offers any type of SPI surface finish, such as A-1, D-2 or D-3.

What’s the right material for each SPI surface finish?

SPI surface/mold finishes produce different results depending on the material you use for injection molding components. The tables below detail how to select the right mold finish and materials for your specific application.

Glossy finish

Material A-1 A-2 A-3
ABS Average Average Good
Polypropylene (PP) Not recommended Average Average
Polystyrene (PS) Average Average Good
HDPE Not recommended Average Average
Nylon Average Average Good
Polycarbonate (PC) Average Good Excellent
Polyurethane (TPU) Not recommended Not recommended Not recommended
Acrylic Excellent Excellent Excellent

Semi-glossy finish

Material B-1 B-2 B-3
ABS Good Good Excellent
Polypropylene (PP) Good Good Excellent
Polystyrene (PS) Excellent Excellent Excellent
HDPE Good Good Excellent
Nylon Good Excellent Excellent
Polycarbonate (PC) Good Good Average
Polyurethane (TPU) Not recommended Average Average
Acrylic Good Good Good

Matte finish

Material C-1 C-2 C-3
ABS Excellent Excellent Excellent
Polypropylene (PP) Excellent Excellent Excellent
Polystyrene (PS) Excellent Excellent Excellent
HDPE Excellent Excellent Excellent
Nylon Excellent Excellent Excellent
Polycarbonate (PC) Average Not recommended Not recommended
Polyurethane (TPU) Good Good Good
Acrylic Good Good Good

Textured finish

Material D-1 D-2 D-3
ABS Excellent Excellent Good
Polypropylene (PP) Excellent Excellent Excellent
Polystyrene (PS) Excellent Excellent Good
HDPE Excellent Excellent Excellent
Nylon Excellent Excellent Good
Polycarbonate (PC) Excellent Not recommended Not recommended
Polyurethane (TPU) Excellent Excellent Good
Acrylic Average Average Average

Need more advice on injection molding custom parts?

Speak with an expert

CNC machining, 3D printing and sheet metal fabrication parts

Frequently asked questions

What are SPI surface finishes?

SPI surface finishes refer to the predominant global surface finish standard set by the Plastics Industry Trade Association (SPI). It covers the 12 grades of SPI mold finishes. You can also refer to SPI surface finishes as SPI mold finishes.


What is the VDI 3400 standard?

While SPI surface finishes are widely used around the world, they aren’t the only mold finishes. The other standard to consider is the VDI 3400 texture or surface finish standard. Set by the Society of German Engineers, it covers 45 grades of texture for injection molded parts.


 

More resources for engineers

Common materials used in injection molding

When producing parts with injection molding, understanding the range of materials that are available is crucial. Find out more about those materials, their properties, and factors to consider when choosing a material for injection molded parts.

Read article

What is overmolding?

Find out about the manufacturing technique used to injection mold a second material over or around a part to create a new one.

Read article

What is die casting?

Want to learn more about die casting? In this article, we’ll take a look at the process, its history and current uses, advantages, design guidelines, and more.

Read article
Injection moulded part

How much does injection molding cost?

In this article, we’ll take a look at common factors that influence the cost of injection molding, including equipment, labor, and materials – as well as tips for reducing manufacturing costs.

Read article

How to avoid common defects in injection molding

What are the most common defects in the injection molding process and how do you avoid them? This article provides six essential design tips for avoid production defects while reducing the cost and lead time of your molded parts.

Read article

What is GD&T? How to reduce manufacturing errors and improve quality

What is Geometric Dimensioning and Tolerancing (GD&T) and how is it used? This article explores the basics of how and when to use GD&T to get the best results out of custom part manufacturing.

Read article

What is design for manufacturability (DFM)?

Design for manufacturing (DFM) means taking a design-first approach to manufacturing. In this article, we look at the overall DFM process, the necessary steps for a successful outcome, examples of DFM done right and how to get the most out of your own processes.

Read article

What is Delrin (POM-H) and what are its material properties?

What is Delrin and why is it unique among the many manufacturing materials available? Delrin, or POM-H (homopolymer acetal), is used in CNC machining, 3D printing and injection molding to create durable, precise components. This article explores Delrin’s properties and how to get the most out of the material.

Read article

What are the common applications of injection molding and its top benefits?

What are the common applications of injection molding? What sets it apart as a manufacturing process? This article covers the key benefits of injection molding and provides insight into whether injection molding is right for your industry’s applications.

Read article
Injection Molding SPI surface finishes

Why is draft angle design essential for injection molding?

Why is it important to design draft angles for injection molding custom parts? This article covers why draft angles are essential and how to design them better to get the most out of your injection molding designs.

Read article
How to design parts for Injection Molding

How do you design parts for injection molding?

How do you optimize part design for injection molding? This complete guide to designing for injection molding provides basic and advanced design tips, including guidelines for creating snap-fits, living hinges and undercuts, and accounting for optimial surface finishes.

Read article
Injection Molding SPI surface finishes

What’s the best SPI surface finish for your injection molded part?

What SPI surface finishes does Protolabs Network have for injection molding custom parts? Check out the standard SPI mold finishes we offer and our material recommendations to get the most out of injection molding.

Read article

Common materials used in injection molding

When producing parts with injection molding, understanding the range of materials that are available is crucial. Find out more about those materials, their properties, and factors to consider when choosing a material for injection molded parts.

Read article

What is overmolding?

Find out about the manufacturing technique used to injection mold a second material over or around a part to create a new one.

Read article

What is die casting?

Want to learn more about die casting? In this article, we’ll take a look at the process, its history and current uses, advantages, design guidelines, and more.

Read article
Injection moulded part

How much does injection molding cost?

In this article, we’ll take a look at common factors that influence the cost of injection molding, including equipment, labor, and materials – as well as tips for reducing manufacturing costs.

Read article

How to avoid common defects in injection molding

What are the most common defects in the injection molding process and how do you avoid them? This article provides six essential design tips for avoid production defects while reducing the cost and lead time of your molded parts.

Read article

What is GD&T? How to reduce manufacturing errors and improve quality

What is Geometric Dimensioning and Tolerancing (GD&T) and how is it used? This article explores the basics of how and when to use GD&T to get the best results out of custom part manufacturing.

Read article

What is design for manufacturability (DFM)?

Design for manufacturing (DFM) means taking a design-first approach to manufacturing. In this article, we look at the overall DFM process, the necessary steps for a successful outcome, examples of DFM done right and how to get the most out of your own processes.

Read article

What is Delrin (POM-H) and what are its material properties?

What is Delrin and why is it unique among the many manufacturing materials available? Delrin, or POM-H (homopolymer acetal), is used in CNC machining, 3D printing and injection molding to create durable, precise components. This article explores Delrin’s properties and how to get the most out of the material.

Read article

What are the common applications of injection molding and its top benefits?

What are the common applications of injection molding? What sets it apart as a manufacturing process? This article covers the key benefits of injection molding and provides insight into whether injection molding is right for your industry’s applications.

Read article
Injection Molding SPI surface finishes

Why is draft angle design essential for injection molding?

Why is it important to design draft angles for injection molding custom parts? This article covers why draft angles are essential and how to design them better to get the most out of your injection molding designs.

Read article
How to design parts for Injection Molding

How do you design parts for injection molding?

How do you optimize part design for injection molding? This complete guide to designing for injection molding provides basic and advanced design tips, including guidelines for creating snap-fits, living hinges and undercuts, and accounting for optimial surface finishes.

Read article
Injection Molding SPI surface finishes

What’s the best SPI surface finish for your injection molded part?

What SPI surface finishes does Protolabs Network have for injection molding custom parts? Check out the standard SPI mold finishes we offer and our material recommendations to get the most out of injection molding.

Read article

Show more

Show less

Ready to transform your CAD file into a custom part? Upload your designs for a free, instant quote.

Get an instant quote