Thread is made from either natural fibers like cotton, silk, and wool, or synthetic polymers like polyester and nylon. Synthetic threads account for about 61% of global production, with natural fibers making up the remaining 39%. The specific material determines how strong, stretchy, and heat-resistant the thread is, which is why different threads exist for everything from sewing a cotton shirt to stitching firefighter gear.
Natural Fiber Threads
Natural threads come from plants or animals. The fibers are spun or twisted into yarn, then twisted further to create thread strong enough to pass through a needle and hold a seam together. Cotton is by far the most common natural thread material, representing about 70% of all natural thread sold worldwide. It comes from the cotton plant’s seed pods, and the highest-quality sewing thread often uses long-staple varieties like Egyptian-grown cotton, which produce smoother, stronger strands.
Silk thread, spun from the cocoons of silkworms, makes up roughly 15% of the natural thread market. It has a natural sheen and is prized for fine garment work and embroidery. Wool thread, sourced from sheep fleece, accounts for about 8%. Beyond these three, linen thread (made from flax plants), hemp, and jute all see use in specialty applications like upholstery, bookbinding, and craft work.
Synthetic Fiber Threads
Most thread today is synthetic, and the raw material for nearly all of it is crude oil. Polyester is the dominant synthetic thread, making up about 50% of all synthetic thread produced. It starts as a petroleum-based polymer: heat and pressure are applied to petroleum-derived acid and alcohol, producing a plastic substance that gets melted and forced through tiny holes called spinnerets to form continuous filaments. Those filaments are then twisted or cut and spun into thread.
Nylon follows a similar path. It’s a polymer built from long chains of carbon-based molecules extracted from crude oil. The chemical reaction produces a nylon salt, which is melted and pushed through spinnerets just like polyester. Nylon thread accounts for roughly 30% of synthetic production. The remaining 20% is rayon, which occupies an interesting middle ground. Rayon is made from wood pulp (a natural source) but undergoes heavy chemical processing, so it’s classified as synthetic or semi-synthetic.
Acrylic thread, while less common for sewing, uses the same basic principle. Fossil fuels undergo a process called polymerization, where heat and pressure transform petroleum or natural gas into a plastic solution that can be drawn into fibers.
How Raw Fiber Becomes Usable Thread
Turning raw fiber into sewing thread involves several steps beyond just spinning. The fibers are first twisted into yarn, then multiple yarns are twisted together to form a “ply.” A 3-ply thread has three twisted strands; heavier 6-ply or 9-ply “corded” threads are common in leatherwork and shoemaking where extra strength matters.
The direction of the twist also matters. Thread twisted in what’s called a Z direction (leftward) works with standard home sewing machines. S-twist thread (rightward) is less common and used in specialized industrial equipment. Getting this wrong can cause the thread to unravel during sewing.
After twisting, cotton threads go through singeing, where they pass through a flame at around 800°C to burn off tiny protruding fibers that would snag in a needle. Threads are then bleached, dyed to match fabric colors, and treated with special waxes or silicone lubricants. That lubrication is critical: a sewing machine needle can reach temperatures above 300°C from friction, and without lubrication, the thread would snap. Decorative threads get additional finishing with gloss-brushing to create a smooth, shiny surface. Some specialty threads for leather stitching or kite flying are polished with starch and softeners.
High-Performance and Industrial Threads
Some applications demand materials far tougher than cotton or polyester. Kevlar thread, made from a synthetic fiber called para-aramid, is on average 2.5 times stronger than nylon or polyester thread of the same size and can withstand temperatures up to 800°F (427°C). It’s used in ballistic gear, racing sails, and protective equipment.
Nomex thread, a related aramid fiber, resists heat up to 700°F (371°C) before it starts to break down. One common construction wraps a Nomex filament core with cotton for easier sewing. Firefighter turnout gear, welding aprons, and military flight suits typically use Nomex or Kevlar thread.
For the most extreme heat environments, PTFE-coated fiberglass thread handles temperatures up to 1,022°F (550°C), though the PTFE coating itself burns away at around 620°F. These threads appear in industrial filtration systems and furnace seals where no organic fiber could survive.
How Thread Thickness Is Measured
Thread thickness is described using weight systems that can seem counterintuitive. The two main standards are Denier and Tex. Denier measures how many grams 9,000 meters of thread weighs, so a higher number means thicker thread. Tex does the same thing but over 1,000 meters: if 1,000 meters of thread weighs 25 grams, it’s Tex 25. Tex is the ISO international standard and is especially common in Europe and for synthetic threads.
In everyday sewing, you’ll more often see “weight” labels like 40wt or 50wt on spools. Confusingly, these work in the opposite direction: a lower number means a thicker thread. A 30wt thread is heavier and more visible in stitching than a 50wt, which is finer and better for blending into seams.
Polyester’s Environmental Footprint
Polyester-based fibers, including thread, now represent 57% of all global fiber production, which exceeded 124 million tonnes in 2023. Because polyester is essentially plastic, it doesn’t biodegrade the way cotton or silk does. Recycled polyester thread, made from melted-down plastic bottles or old textiles, is growing as an alternative. However, less than 1% of fibers currently come from recycled textiles, leaving enormous room for the industry to close that loop. Recycling methods range from mechanical processes (grinding and remelting the plastic) to chemical approaches that break the polymer back down to its basic building blocks before rebuilding it into new fiber.