What counts
Nap is a pile or brushed surface, such as velvet, corduroy or minky. Stroked one way it feels smoother and looks lighter; the other way it looks darker. A directional print has a design that only works one way up, such as animals that would stand on their heads if a piece were turned.
Why it needs more fabric
On ordinary fabric, pieces can be turned end to end to fit them closer together. With nap or a one-way print, every piece has to face the same way, so pattern envelopes give separate “with nap” cutting layouts, and the yardage can go up. Fabrics that must be matched, such as plaids, stripes and large motifs, also need extra.
For quilt backings, a directional print may rule out the seam direction that uses the least fabric. Check the quilt backing calculator’s layout before you buy.