Knowledge base Appendix

Injection Molding SPI surface finishes

Written by
Alkaios Bournias Varotsis
Tables with the standard SPI mold finishes and material recommendations to achieve best results.

SPI Mold Finishes

Learn more about the Injection molding surface finishes, in the main article here.

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 (Society of Plastic Industry) standards

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Material recommendations

Not every mold finish produces the same results with every material. Use the tables below as guidelines to select the right mold finish/material combination for your 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

Written by
Alkaios's picture
Alkaios Bournias Varotsis

Mechanical Engineer at 3D Hubs. More questions? Email me!

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