In chemical processing, a "packed bed" is a hollow tube, pipe, or other vessel that is filled with a packing material. The packing can be randomly filled with small objects like "Raschig rings" or else it can be a specifically designed "structured packing".
The purpose of a packed bed is typically to improve contact between two phases in a chemical or similar process. Packed beds can be used in a chemical reactor, a distillation process, or a scrubber.
The term structured packing refers to a range of specially designed materials for use in absorption and distillation columns and chemical reactors. Structured packings typically consist of thin corrugated metal plates or gauzes arranged in a way that they force fluids to take complicated paths through the column, thereby creating a large surface area for contact between different phases.