Further work on bulk-related "optical" carpet streaks is reported here, focusing on their instrumental characterization. Texturing process conditions have been adjusted to create bulk variation in both commercial staple and bulk-continuous-filament (BCF) products. For the staple items, bulk is characterized in the fiber, in the pre-and postheatset yarns, and in the carpet tuft itself. Both the staple fiber and heat-set yam methods are new. Yarns from both carpet manufacturing processes have been implanted as tuftlines into multiple carpet backgrounds, each background made with different levels of bulk. Sixty such staple and 144 BCF implants, most obvious streaks because of their bulk differences, have been evaluated by graders for intensity and shade; these grades correlate well with those ranked instrumentally ( R 2 = 0.91 and 0.94, respectively) and, for the staple products, with various measures of bulk ( R 2 from 0.78 to 0.95).Goniophotometry has also been used to ascribe the unique optical effect commonly seen in bulk-related streaks, that of changing shade with view direction, to the carpet's surface filament configuration.Streaks in cut-pile saxony carpets can cause uniformity problems that significantly impact quality and manufacturing yields. Commercially, one important problem is bulk variation between tuftlines: light falling on a streak tuftline scatters differently from that falling on the general background. This phenomenon is the same one responsible for the grass-cutting patterns you see in a televised baseball game. There, the blades of grass in adjacent, mowed rows orient in opposite directions with the change in mower direction, and the resultant difference in light scattering behavior causes a striped pattern. Another common example is the shade dependence on a carpet's pile lay: a carpet appears darker when the lay of the pile faces the viewer.As Figure 1 shows, when bulk variations are made different enough-here in velour fabric, but also in cut-pile saxony carpets (see Figure 1 of reference 14 )-a similar phenomenon occurs. LeGault [9, 10 described a variety of causes that can produce these nondye-on-fiber streaks, known collectively in the carpet industry as &dquo;optical&dquo; streaks. Here, we will limit our discussion to those &dquo;optical&dquo; streaks related to bulk.The bulk-related streak differs from a streak caused by dye-on-fiber differences in one fundamental way. Its intensity and shade both depend on how you view the streak: a low-bulk tuftline appears dark when viewed in the &dquo;against-pile&dquo; direction, but frequendy appears light when viewed from the opposite &dquo;withpile&dquo; direction. By contrast, Baxley and Miller [2] ] and Gibson et al. [ 4 ] have created actual dye-on-fiber streaks by varying heat-set conditions. Figure 2 of ref-FIGURE 1. A velour acrylic fabric viewed against the pile,showing several bulk-related optical streaks.