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SPI Finish
What is SPI Finish?
SPI Finish refers to the surface finish standards defined by the Society of the Plastics Industry (SPI)—now known as PLASTICS—for injection mold surfaces. These standards classify mold cavity finishes into different grades ranging from high-gloss optical finishes to textured or matte surfaces.
The SPI system includes four main categories (A, B, C, D), which are produced using different processes such as diamond polishing, fine sanding, stone finishing, or dry blasting.
SPI finishes allow designers, mold makers, and injection molders to communicate surface requirements clearly, ensuring consistency in part appearance, texture, release characteristics, and overall quality.
Others Surface Treatment Choice For Parts
Anodizing
Electroplating
Spraying
Sandblasting
PVD
Pad Printing
Hot Stamping
Mold Polishing
Laser Engraving
Silk Screen Printing
FAQ Of SPI Finish
Visit our FAQ center for more questions.
What are the main categories of SPI finishes?
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A Series (A-1 to A-3) – High-gloss, optical-grade finishes using diamond polishing
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B Series (B-1 to B-3) – Semi-gloss finishes created by sanding
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C Series (C-1 to C-3) – Matte surfaces created using fine stones
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D Series (D-1 to D-3) – Rougher textures created through dry blasting or grit blasting
Why is SPI finish important for injection molded parts?
SPI finish directly affects part appearance, mold release, friction, post-processing needs, and surface defects. A precise finish ensures consistent production quality and meets aesthetic or functional requirements.
Does SPI finish affect molding performance?
Yes. Higher-gloss finishes (A series) improve release for glossy products but require more maintenance. Matte or textured finishes (C/D series) help hide sink marks, flow lines, and minor defects but may require higher injection pressure.