Effects of yarn size and blood drop size on wicking and bloodstains in textiles

Bloodstain pattern analysis (BPA) for stains found on non-porous surfaces has matured into a powerful forensic science tool based on fluid mechanics principles. The same cannot be said when bloodstains are found on porous substrates, such as textiles. This is partially due to the complex nature of textiles with tens of thousands of different materials in addition to unknown wear characteristics. In this study, three single jersey knit fabrics were manufactured from 100% cotton ring-spun yarns of linear densities of 12, 20, and 30 Ne (492, 295, and 197 dtex, respectively) and nearly identical twist multipliers. Single drops of porcine blood of 2, 10, 30, and 60 µL were allowed to fall 1 cm (to eliminate the impact of blood velocity) onto each fabric to understand the effects of yarn size on wicking and bloodstains. The size of the stain was then measured and compared for different fabrics and blood drop sizes. Wicking of blood into the fabric was fastest for the largest yarn fabrics, but more extensive wicking occurred on finer yarn fabrics resulting in much larger stains. All stains were highly altered due to wicking of blood. The findings from this paper might help the forensic scientists in understanding wicking in textiles and comparing stains on different textiles to gain a better understanding of bloodstains on textiles.