In the field of weft‑knitted fabrics, elasticity has always been a core indicator of quality and wearing comfort. Traditionally, fabric elasticity relies mainly on spandex‑core or wrapped yarns. However, spandex has clear drawbacks – it tends to degrade after repeated washing, exposure to sunlight, or contact with chlorine and high temperatures. Wearers often find that after many wears and washes, areas such as knees and elbows become loose, baggy, and deformed. Moreover, spandex’s elasticity declines with repeated stretching and over time – a phenomenon known as “elastic fatigue.” These pain points have driven the industry to seek an alternative solution that provides durable elasticity without the need for spandex.
The emergence of Sorona® yarn offers a fundamental solution to the above problems. DuPont™ Sorona® is a revolutionary bio‑based polymer (PTT fiber). Its key technology is that 37% of its raw materials come from annually renewable plant resources – 1,3‑propanediol (PDO) produced by fermenting corn sugar, which is then polymerized with terephthalic acid. This gives Sorona® significant environmental benefits: compared with petroleum‑based nylon, its production process reduces petroleum resource consumption by 37%, energy use by 44%, and greenhouse gas emissions by 59%.
In terms of performance, Sorona®’s unique molecular structure (a “Z‑shaped” conformation) gives it spring‑like elastic deformation capability, and this conformational change is reversible – the fiber returns to its original shape when the external force is removed. Specifically, Sorona® yarn provides 15–20% natural stretch, with an elastic recovery rate of over 92% at 300% elongation, achieving comfortable stretch and shape retention without relying on spandex. Unlike spandex, Sorona®’s elasticity comes from the fiber’s molecular structure itself, not from an external sheath. Therefore, it does not easily lose elasticity after repeated washing and stretching, and its shape retention is significantly better than that of traditional spandex fabrics.
What is more noteworthy is that Sorona® is naturally well‑suited to the weft‑knitting process. Weft knitting machines form loop structures by the knitting action of needles in the horizontal direction, which requires the yarn to have good flexibility and dimensional stability. Sorona® yarn combines a soft hand feel (close to cotton, with a silky smoothness), excellent color fastness (can be dyed at atmospheric pressure and boiling temperature), and wrinkle‑free, easy‑care properties, making it run smoothly and efficiently on circular weft knitting machines. In practical development, companies can use 100% Sorona® yarn to weft‑knit naturally stretchable jersey fabrics, or blend Sorona® with cotton, modal, viscose, and other fibers in different ratios to develop various fabric structures such as plain and interlock on single‑knit or double‑knit machines. Industry practice shows that weft‑knitted fabrics made from Modal/Sorona blended yarn on circular knitting machines exhibit good elastic recovery, low shrinkage, and a smooth, soft hand feel, making them suitable for high‑end applications such as T‑shirts, baby wear, and underwear.
From an industry trend perspective, “ammonia‑free stretch” has become an important innovation direction in textiles. Since Sorona® introduced the “ammonia‑free stretch” concept in the Chinese market in 2012, it has gradually moved from being unknown to being adopted in high‑end professional segments such as sportswear, casual wear, and outdoor gear, and has established long‑term partnerships with industry leaders like Anta. In July 2025, the industry held a dedicated “No Stretch Without Fabric, New Elasticity Without Ammonia” seminar on the development of ammonia‑free elastic fabrics, exploring the broad application prospects of non‑spandex elastic fibers such as Sorona® stretch composite yarns in sportswear, yoga wear, outdoor equipment, and more.
In summary, using Sorona® yarn as a weft‑knitting raw material – with its plant‑based bio‑origin, durable mechanical elasticity endowed by its spring‑like molecular structure, and excellent compatibility with the weft‑knitting process – has truly ushered in a new era of ammonia‑free stretch fabric. It achieves fabric elasticity that can “stretch out and spring back,” enabling weft‑knitted fabrics to have long‑lasting, comfortable stretch and outstanding shape retention without depending on spandex.
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