Using gravity to initiate flow in the discharge of solid materials from bins and hoppers is the simplest, and often best, approach to solving solids-handling challenges. However, not all solid materials flow well by gravity alone. The propensity for fine solid materials to cake can lead to flow problems that will adversely affect your process. For situations where material caking disrupts gravity flow, a range of flow aid approaches are available to solve a variety of flow issues. This article discusses the operation of passive and active flow aids, and points out considerations for their use.