SPI Mold Finish – Injection Molds

SPI (Society of Plastic Industry) establish standards for plastic part finishes. It defines the polishing standard on mold finish. 

Nowadays, china’s Ra standard is very much in line with SPI. Chinese manufacturing industry is using chinese standard equivalent to SPI. 

In this article we will discuss various available finishes in SPI standard.

Finish SPI Standard Finish Method Surface Roughness (Ra Value)
Very High Glossy Finish A1 6000 Grit diamond buff 0.012 to 0.025
High Glossy Finish A2 3000 Grit diamond buff 0.025 to 0.05
Normal Glossy Finish A3 1200 Grit diamond buff 0.05 to 0.1
Fine Semi Glossy Finish B1 600 Grit Paper 0.05 to 0.1
Medium Semi Glossy Finish B2 400 Grit Paper 0.1 to 0.15
Normal Semi Glossy Finish B3 320 Grit Paper 0.28 to 0.32
Fine Matte Finish C1 600 Grit Stone 0.35 to 0.4
Medium Matte Finish C2 400 Grit Stone 0.45 to 0.55
Normal Matte Finish C1 320 Grit Stone 0.63 to 0.70
Satin Textured Finish D1 600 stone prior to dry blast glass bead #11 0.8 to 1.0
Dry Textured Finish D2 400 stone prior to dry blast #240 oxide 1.0 to 2.8
Rough Textured Finish D3 320 stone prior to dry blast #24 oxide 3.2 to 18.0
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