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

What SPI surface finishes does Hubs 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 Hubs?

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
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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
Hubs 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



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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.


 

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