A clever heuristic algorithm by Dietrich and Yakowitz ("A rule-based approach to the trim-loss problem," Int. J. Prod. Res. 20, pp. 401-415, 1991) is employed in 2NA for packing smaller rectangles within larger rectangles. This algorithm is very fast, so 2NA tries to make extensive use of it. A typical speed for packing rectangles inside a larger rectangle is a few milliseconds.
A nest of smaller rectangles packed within a larger one might look like the following: