Kevlar is best known as the incredibly strong material used by the military and SWAT teams in their body armor and helmets. This reputation as “bulletproof” has sometimes led to a bit of confusion as to the purpose of putting Kevlar in cables. Some reviewers have taken such cables to the firing range and been disappointed when the cable couldn’t stand up to being shot by a handgun at close range. Of course the purpose of adding Kevlar to cables isn’t to make them resistant to gunfire, it’s way more useful than that (for the ordinary consumer at least!). Let’s have a closer look at this fascinating material and see what it has to offer the world of electronics beyond “bulletproof”.
Kevlar? Aramid? Twaron?
One point worth making clear is that the name Kevlar is actually a trademark of DuPont, meaning that legally you can only call your material Kevlar if you buy from them. There are various other trade names out there for the same material, such as Twaron and Technora, but we prefer to use the actual name for this type of material, “aramid fiber“.
Aramid fiber has a pretty impressive set of properties. In terms of density (and therefore weight) aramid is comparable to linen and even nylon, yet it is also significantly stronger than both steel and diamond in terms of tensile strength. Tensile strength is a measure of how well a material stands up to being stretched or pulled apart, in other words exactly the kind of property you’d want in a durable cable. Despite being close to unbreakable it’s still barely any more dense than nylon, a material used in women’s stockings. This strength to weight ratio is pretty much unbeatable across material science and explains aramid’s popularity in extreme equipment.
Why is it so strong?
It’s all about the chemistry. Other polymers are relatively weakly bonded and are free to move around, creating a somewhat chaotic structure that can described as being like “spaghetti”. Aramid is unique among polymers in that the chains remain rigid and bond to each other perpendicularly through super-sturdy hydrogen bonds. This structure is extremely difficult to break, it takes a huge amount of energy to cut or penetrate a solid piece of aramid fiber. The strong hydrogen bonds also mean that aramid fiber is impossible to melt and will only begin to suffer damage at temperatures in excess of 450°C.
How does it improve a cable?
It’s obvious why the military would be interested in such an indestructible material, but what is the advantage of using something as exotic as aramid fiber in cables? As we covered in detail in an earlier article, the main cause of cable failure is damage to the internal wiring through bending stresses. With an aramid strengthened cable this kind of damage is massively reduced as the forces are dissipated through the strong fibers rather than the vulnerable wiring. The aramid coating also means the cable is much less likely to bend sharply or kink in the first place, despite it remaining easily flexible.
Dismissed as a marketing gimmick by some, there are in fact significant advantages to be had through reinforcing cables with aramid fiber (Kevlar). The high tensile strength is the perfect property for strengthening cables, hugely reducing the damage that is usually suffered through bending and twisting, and all while adding barely any weight to the cable. It’s these properties that make aramid fiber so attractive to those aiming to produce long lasting, premium cables.