Dupion silk is rougher than regular silk and contains knots and irregularities where the fibers from two different kinds of cocoon are combined. Because there is a shortage of supply of the double cocoons used in dupion silk production, an efficient method of producing double cocoons is needed. A commercial race named N-tama×C-tama, which has a high percentage of double cocoons, has been reported. However, this race has defective reelability. We therefore bred a new race, J701×C701, with improved reelability. About 40% of the larvae of J701×C701 made double cocoons, and the performance characteristics of silk from this race were almost the same as those of silks from ordinary commercial races. The knots of dupion silk reeled from J701×C701 cocoons were slightly smaller than those of J137×C146. The fukurami (fullness and softness) value of fabric made from J701×C701 dupion silk was smaller than that of fabric made from J137×C146 silk. In contrast, the shari (crispness value was greater. We have given the name Shurimaru to J701×C701.