The fuller's teasel (the cultivar group "Dipsacus fullonum" Sativus Group; syn. "D. sativus") was formerly widely used in textile processing, providing a natural comb for cleaning, aligning and raising the nap on fabrics, particularly wool. It differs from the wild type in having stouter, somewhat recurved spines on the seed heads. The dried flower heads were attached to spindles, wheels, or cylinders, sometimes called teasel frames, to raise the nap on fabrics (that is, to tease the fibres). By the 20th century, teasels were largely replaced by metal cards, which could be made uniform and do not require constant replacement as the teasel heads wear. However, some people who weave wool still prefer to use teasels for raising the nap, claiming that the result is better; in particular, if a teasel meets serious resistance in the fabric, it will break, whereas a metal tool would rip the cloth.