Southern Polyurethanes (SPI) Flattening Agent is used flatten clear coats and single stage paints.  The Southern Polyurethanes Universal Flattening Agent (SPI 950-4) is a professional-grade additive designed to reduce gloss in clear coats, primers, and single-stage topcoats. Ideal for custom finishes, restorations, and OEM refinishing, this flattening agent gives you complete control over sheen—from subtle satin to full matte—without compromising durability, UV protection, or chemical resistance. Mix it in to achieve anything from satin to full matte finishes without sacrificing durability or UV protection.  Available in quarts only.