Anti-foam AF-4 is a "surface tension relieving" agent recommended as an additive for many polyurethane systems. Its purpose is to assist in the vacuum degassing procedure (deaeration), by reducing the surface tension of entrained air bubbles in the resin mixture. Also, it assists in better resin flow and wet out in molds.
Note: AF-4 does not replace the need for pulling a vacuum on casting polyurethanes to eliminate air.
The term anti-foam refers to the elimination or more rapid reduction of foaming action during the vacuum de-gassing process. Antifoam AF-4 is completely silicone free and does not affect the color, appearance or bond ability of cured urethane parts.