Kevlar is such a successful material due to its tremendous tensile strength (the amount of stretching it can withstand before breaking). The reason why it is so strong is mainly due to the straight fibres that it possesses. In order to fully understand this concept, crystallinity must be taken in to account.

Cristallinity is a property of polymers. When a polymer is not arranged in an orderly manner it is called amorphous. Amorphous polymers are polymer chains that are tangled up and do not follow a strict pattern. They give the polymer the ability to bend without breaking, an important part in Kevlar.

If a polymer is arranged in a neat, orderly manner the polymer is considered crystalline. Crystallinity gives the polymer strength, but crystallinity tends to make the polymer extremely brittle. For instance, Plexiglas is easily susceptible to shattering due to its high crystallinity and weak amorphousness. Yet Lexan is much more shatter resistant due to its lower crystallinity and higher amorphousness. By mixing the two characteristics, sacrificing strength for flexibility or flexibility for strength, an ideal substance can be created. This is how Kevlar came to be.

When scientists look for high tensile strength fibres, they search for a polymer with trans- conformations and try to avoid ones with cis- conformations. Cis- conformations can be a problem due to the fact that they have a tendency to cause unwanted bends in the polymer chain. Bends are a problem due to the fact that they weaken the fibres and lower the strength and crystallinity. Trans- conformations are wanted and useful thanks to the fact that they create a fully stretched out and straight polymer chain. This in turn creates a very strong crystalline polymer with an almost perfect mix of amorphousness and crystallinity.

With many polymers, even the slightest amount of energy can change the conformations. Kevlar is an exception. It tends to keep its trans- conformations and rarely form cis- conformations. This is due to the shape of the aromatic rings that Kevlar possesses. When Kevlar attempts to bend into the cis- conformation, the hydrogens on the aromatic rings cannot be manipulated to fit in the gap, they take up too much space. This is why Kevlar tends to remain in the trans- conformation. The aromatic hydrogens have plenty of room and with this trans- conformation and the molecule tends to stay in a nice and long fibre.

Another important characteristic about Kevlar is that it can make strong types of intermolecular forces, hydrogen bonds. Hydrogen bonds are responsible for keeping multiple fibre strands "glued together". The polar amide groups on adjacent chains bond together with magnetic charges. The oxygen atom can be considered negative and the hydrogen atom positive. The negative atom attracts the positive atom and a hydrogen bond is created.

All these properties give Kevlar many advantages over other polymers. It has a tremendously high tensile strength and is five times stronger than steel. Underwater, Kevlar is up to 20 times stronger than steel! Temperature-wise, Kevlar exceeds the performance of many other materials. It can withstand temperatures up to 300°C while retaining its strength properties. Even at -196°C Kevlar shows no signs of embrittlement or loss of strength. Almost all solvents are ineffective at degrading Kevlar except the few powerful acids.

However, Kevlar is not indestructible. One of the factors that can impede and degrade its performance is ultraviolet light. The degradation is small though, only the outside layer is affected and not the inside one. Even the performance is not affected too much; the Kevlar retains most of its strength and rigidity.