Baffles based on heat activated foams have found increasing use as body cavity filler to inhibit noise propagation through hollow body channels, such as pillars in passenger cars. However, most conventional expandable foams tend to sag, deform and foam randomly, unless they are supported or sandwiched by rigid plastic or metal plates. The uncontrolled foaming reduces the reliability of cavity sealing for fumes, water and noise. The sandwich designs add to the part weight and increase cost unnecessarily. This paper introduces a heat activated expandable foam with programmed directional control during expansion. The directional control is especially useful for filling cavities such as pillars with complex geometry or sharp pinch-welded corners; it also eliminates the need for sandwich design. To demonstrate the effectiveness of the foams with directional control, the dynamics of cavity filling was studied by comparing programmed foaming with random foaming. The acoustic test result of expanded programmed foams is presented. Other advantages of programmed foams are also discussed.