In the skiving process, fins are machined using special skiving or scraping tooling, whereby precisely sliced layers from an metal block are bent at the base of the slice to form slender curved fins. Since the fins and base are an integral unit, the interface resistance seen in folded and bonded heat sinks is not present. This process was originally developed to manufacture sparse natural convection arrays, but recent efforts have been focused towards achieving tighter fin spacing, necessary for forced convection cooling. Aluminum 6063 is the preferred material on account of its superior machinability and strength, but copper arrays can also be made.