Most bras are made from a blend of nylon, polyester, and spandex (also called elastane or Lycra), with each fiber handling a different job. Nylon and polyester form the smooth, durable shell of the cups and straps, while spandex provides the stretch that lets a bra move with your body and snap back into shape. Beyond these core fabrics, a typical bra contains several other materials: metal or plastic underwires, foam or knitted padding, and metal hardware for the closures and adjusters.
The Main Fabrics: Nylon, Polyester, and Spandex
Nylon and polyester are the workhorses of bra construction. Both are synthetic, lightweight, and resistant to wear. Nylon has a slightly silkier feel against the skin, which is why it’s commonly used as a cup lining. Polyester is often the base fabric for cups because it holds its shape well and resists shrinking. A typical cup fabric might be 100% polyester in a tricot knit, with stretch that comes from the weave pattern rather than from elastic fibers.
Spandex is what makes a bra feel flexible rather than rigid. It can stretch up to 600% of its original length and spring back without losing its shape. In everyday bras, spandex typically makes up a small percentage of the cup fabric but a much larger share of the band. The band needs significant stretch so you can breathe and move comfortably, which is why it’s usually made from power mesh (also called power net) that stretches 30 to 50% in multiple directions. Sportswear and bras with high compression can contain 15 to 40% spandex, while lighter styles use less.
Cotton, Silk, and Bamboo Options
Not every bra is purely synthetic. Cotton bras exist for people who prefer a natural fiber against their skin, and they’re popular with anyone who finds synthetics irritating. Cotton breathes well and feels soft, but it absorbs moisture rather than wicking it away, so it can feel damp after sweating. It also loses its shape faster than synthetic blends unless it’s mixed with a small percentage of spandex.
Silk is used in some luxury bras for its smooth, cool feel, but it’s delicate and expensive, so it remains a niche choice. Bamboo fabric has gained popularity as a middle ground: it feels buttery soft from the first wear, wicks moisture effectively, and naturally resists odor. Bamboo bras and underwear stay fresh longer and reduce chafing on sensitive skin. One trade-off is that bamboo weakens when saturated, so these bras need gentle handling during washing.
What Gives Bra Cups Their Shape
Molded bra cups get their structure from polyurethane foam, a lightweight material that can be heat-pressed into a smooth, rounded shape. Foam cups provide consistent coverage and a seamless look under clothing, but they don’t breathe particularly well. Air has a harder time passing through dense foam, which can make these bras feel warm.
A newer alternative is spacer fabric, a three-dimensional knitted textile with two outer layers connected by fine threads in the middle. This creates a cushion of air between the layers. Research comparing the two found that spacer fabric cups provide compression and support comparable to foam, but with significantly better airflow. Spacer fabric cups let substantially more air through than foam, which translates to a cooler, more comfortable wear, especially in warm weather.
Underwires, Hooks, and Hardware
The underwire in a traditional bra is most commonly stainless steel. It’s strong, holds its curve, and resists bending or snapping. To prevent rust and keep the metal from irritating your skin, steel underwires are coated in a thin layer of plastic or nylon. This coating also helps the wire slide into its fabric casing during manufacturing and reduces the chance of it poking through over time.
Some bras replace metal entirely with underwires made from high-strength plastic like nylon or polyethylene. These are lighter and more flexible, bending with your body as you move. They’re a common choice in bras designed for sensitive skin or for people who find metal wires uncomfortable. A third option is resin-coated metal wire, which splits the difference: you get the strength of metal with a softer, more flexible outer layer that lowers the risk of allergic reactions.
The hook-and-eye closures on the back band are typically stamped from metal and coated with nylon for durability and a smooth feel. Strap adjusters and rings are made from similar materials, sometimes all-plastic in less structured bralettes.
Sports Bra Fabrics
Sports bras prioritize moisture management and shape recovery. The base fabrics are still nylon and polyester blends with spandex, but they’re engineered with specific finishes that pull sweat away from your skin and spread it across the fabric’s surface so it evaporates quickly. Brands use proprietary names for these technologies, but the underlying principle is the same: the fabric is either treated with a hydrophilic (water-attracting) finish on the outer layer or constructed with channels that move moisture outward.
Four-way stretch fabric is standard in sports bras, meaning it stretches both lengthwise and crosswise. This allows the bra to move with you during overhead reaches, twists, and impact without binding or shifting. Compression-style sports bras use tighter, denser knits with higher spandex content to press breast tissue firmly against the chest wall. Some high-performance sports bras also incorporate antimicrobial treatments to limit bacterial growth from sweat.
Seamless and 3D-Knitted Construction
Traditional bras are cut from flat fabric panels and sewn together, but seamless bras are produced on circular knitting machines that create the entire garment in one piece. These machines can vary the knit density, stretch, and thickness across different zones of the bra without any cutting or stitching. The result is a bra with no seams to rub against skin and a more precise fit in areas that need more or less support.
Seamless bras are typically knitted from blends of nylon and spandex, though some performance versions use wool-nylon-spandex combinations. Wool adds natural moisture responsiveness, meaning the fabric can react to perspiration by changing its structure slightly, while nylon provides durability and spandex delivers stretch.
Sustainable and Certified Materials
Recycled polyester and recycled nylon, made from post-consumer plastic bottles or discarded fishing nets, are increasingly common in bras from sustainability-focused brands. These recycled fibers perform identically to virgin synthetics but reduce the demand for new petroleum-based materials.
TENCEL is a fiber spun from sustainably harvested wood pulp. It’s produced through a closed-loop process that recycles 99% of the water and solvents used in manufacturing, making it one of the lowest-impact textile fibers available. TENCEL bras feel silky and breathe well, similar to bamboo but with a more controlled supply chain. Brands using certified TENCEL can trace the fiber from tree to finished thread.
If chemical safety matters to you, look for the OEKO-TEX Standard 100 label. This certification means the fabric has been tested for substances harmful to human health, including heavy metals, pesticides, and formaldehyde. The testing criteria are stricter for products with direct, prolonged skin contact (like bras) than for outerwear. OEKO-TEX also bans PFAS (“forever chemicals”) and most flame retardants across all certified products, going beyond the requirements of many national regulations.