Compared to other species of tree used in hardwood flooring, black walnut is relatively soft. It is also relatively dark, lending floors made with it a characteristic warmth. It is also relatively more expensive than other woods.
The suitability of a species of wood for use as flooring is measured using a process called the Janka hardness test. The Janka test measures the force required to embed a standardized steel ball halfway into a piece of wood, measured in a unit called pounds-force in the United States. Black walnut scores a 1010 on the scale. By comparison, balsa wood, a very soft wood, scores 100, while Australian Buloke, an extremely hard wood, scores a 5060.
Other common hardwood flooring species are white oak and maple, which score a 1360 and 1450, respectively. Also available for higher-traffic floors is Brazilian walnut, which scores a 3684 on the Janka test. Brazilian walnut is more expensive than American walnut, which is itself more expensive than oak, maple and other species.
American walnut also offers somewhat more color variation than other woods. There is significant difference between the sapwood (the outer wood) and the heartwood, meaning that floors made with this material can have greater tonal and pattern variations than other materials.