<p>This research provides a comprehensive investigation of the auxetic yarn (AY) production process, with the primary objective of developing an auxetic complex yarn that demonstrates a significant auxetic effect, emphasizing the distinctions associated with different core yarn quantities (1–8) in conjunction with a single wrap yarn. Two distinct classes of auxetic yarns (AYs) were developed through the combination of 1680 D spandex core yarn with either 150 D/3 or 210 D/3 polyester wrap yarn. AYs were fabricated in a high-speed braiding machine. An extensive examination was conducted regarding the tensile and deformation characteristics of the yarn to ascertain its negative Poisson ratio (NPR). Calculations of Poisson's ratio were conducted utilizing image processing software (Vistar Image 4.0 for Digital Camera). The findings indicate that axial stretching considerably affects the NPR. At the same time, lateral expansion is contingent upon the specific type of yarn, including variations in core yarns. Additional factors that affect these outcomes encompass the rotational speed of the spindle, the number of core yarns, and the linear density of the wrapped yarn. The prepared AYs can be employed in many applications, including personal and sports protective equipment.</p>