Commercially available compact heat exchangers are currently fabricated in several steps by joining multiple tubes, or by independently fabricating and joining fluid channels. Friction stir channeling (FSC) is a simple and innovative technique of manufacturing heat exchangers in a single step by creating continuous, integral channels in a monolithic plate in a single pass. FSC relies on the frictional heat generated between the tool material and the metal workpiece to soften and deform the material to facilitate the creation of a continuous channel. The channel shape, size, and integrity depend on the processing parameters and the tool design. In this paper the structural characteristics and the relationship between the channel features and the processing parameters are discussed. FSC is being developed as a technique for manufacturing heat exchangers. The channel is characterized by roughness features on the inside, which can be analyzed using optical microscopy techniques.