Aramid fibre

An aramid is a polyamide — the same amide linkage as nylon — built from aromatic rings instead of flexible chains. The rings make the molecule a rigid rod, the rods line up along the fibre axis during spinning, and hydrogen bonds lock the sheets together. The result is a fibre with roughly five times the tensile strength of steel per unit mass.

The two families do different jobs and are routinely confused. Para-aramid — Kevlar, Twaron — is the strong one, and is what body armour and composite reinforcement are made of. Meta-aramid — Nomex — is much less strong and is inherently flame resistant, and is what a firefighter's or racing driver's clothing is made of.

The weakness is anisotropy taken to an extreme. Along the fibre it is exceptional; across it, it is weak, and it fails in compression by kinking rather than breaking. An aramid composite is superb in tension and poor in compression, which is why it is often hybridised with carbon fibre rather than used alone.

Spun from a liquid crystalline solution in concentrated sulfuric acid — the molecules are already aligned in the dope before they reach the spinneret, which is the discovery the fibre rests on. The acid is then washed out and recovered.

It cannot be melt spun; it decomposes before it melts. Cutting and machining aramid fabric is notoriously awkward because the fibres that resist a knife also resist scissors, and specialised shears exist for the purpose.

Soft body armour and helmets, where layers of woven fabric catch a projectile and spread its energy. Cut-resistant gloves and sleeves. Composite reinforcement in aircraft, boats and pressure vessels. Tyre reinforcement belts. Ropes and mooring lines with a fraction of steel wire's weight. Brake and clutch friction materials, where it replaced asbestos. Fibre-optic cable strength members.

Meta-aramid, separately: firefighting and industrial flame-resistant clothing, racing suits, and electrical insulation paper in transformers.

Discovered at DuPont in 1965 by Stephanie Kwolek, who was working on a stiff-chain polyamide and produced a solution that was cloudy and thin rather than the clear viscous syrup expected. It looked like a failed batch, and the technician operating the spinneret was reluctant to run it. Spun, it gave a fibre stiffer and stronger than anything then known.

The cloudiness was the liquid crystalline ordering — the molecules were already aligned in solution — which is why the discovery mattered as chemistry and not only as a product. Commercial Kevlar followed in 1971, and body armour shortly after.

Energy intensive to produce and effectively not recycled: aramid appears embedded in composites, laminated into armour panels and blended into friction materials, and separating it from those is not economic.

It degrades under ultraviolet light, losing strength over months of direct exposure, so aramid rope and fabric are jacketed or dyed. Body armour carries an expiry date for related reasons — the fibre's ballistic performance falls with age, moisture and repeated flexing, and a vest past its date is not certified even if it looks intact.