Injection Molding Surface Finish: SPI Grades and Textures Explained
Oct 26, 2026
Surface finish is one of the first things a customer notices and one of the last things a project team specifies. In most injection molding projects the finish ends up as a single line on the drawing — or worse, as a sentence in an email — and by the time the first samples arrive it is too late to change it cheaply. This guide explains the SPI finish standard, the texture systems used alongside it, how finish interacts with part design and molding, and how to specify it so the mold is built right the first time.
Why Surface Finish Is a Tooling Decision
The finish you see on a molded part is a copy of the cavity surface, transferred under heat and pressure. That has a practical consequence: finish is set when the steel is polished or etched, not when the parts are molded. Changi...
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