Spider silk does not twist because it is a non-helical fiber, meaning it lacks a regular, spiraling structure. Unlike many other types of fibers, such as cotton or wool, which are composed of twisted strands of cellulose or protein molecules, spider silk is made up of long, straight chains of amino acids that are held together by strong chemical bonds. This unique molecular structure gives spider silk its remarkable strength and elasticity without causing it to twist.

Additionally, the silk produced by spiders contains a special type of protein called "spidroin." This protein is spun into fibers with a unique molecular architecture, which prevents the silk from twisting or kinking. The silk proteins self-assemble into a liquid crystal state, where the molecules align themselves in an orderly fashion. This alignment creates a strong, stiff fiber with a high tensile strength, yet it remains flexible and does not twist.