Nylon 6 and Nylon 66 are two of the most popular polymers used in the plastics, automotive and textile industries. As the similarity between their names suggests, the two share some properties, but there are also key differences between these two types of nylon. An exploration of the different chemical structures of the two materials can help you understand which jobs are best performed by Nylon 6 and which are better handled by Nylon 66.

Both Nylon 6 and Nylon 66 are polyamides, which means they are molecules whose repeating units are linked by amide bonds. Some polyamides, such as silk, can be found naturally, but nylons are made in a lab. There are several types of nylons, but Nylon 6 and 66 are two of the most popular ones thanks to being relatively lightweight while also strong and durable.

Though Nylon 6 and Nylon 66 share some physical properties, their chemical structures are different. Nylon 6 is made from a single type of monomer, called caprolactam. Caprolactam’s formula is (CH2)5C(O)NH. Since its discovery in the 1800s, global demand of caprolactam has grown to more than 5 million tons per year, almost all of which goes toward making Nylon 6.

Nylon 66 is made up of two monomers, adipoyl chloride and hexamethylene diamine. The strong chemical bond between the two forces gives Nylon 66 a more crystalline structure, making it slightly stiffer and better equipped to handle more heat than Nylon 6.

The first popular commercial use of nylon in the United States began in the early 1940s when the material was used to produce stockings for women. When World War II began and many of the country’s resources were geared toward helping the war effort, scientists took to the lab to manufacture new, stronger materials. The result was the creation of nylon varieties like Nylon 6 and Nylon 66, which are far more durable than the nylon used for stockings.

Nylon 6 is used in all kinds of products including hammerheads, plastic cutting boards, rope and circuit breakers. One of its greatest strengths is its flexibility, which makes it a suitable metal replacement in products such as car parts. It’s also a bit more lustrous than Nylon 66, so it’s more commonly used in items such as radiator grilles, stadium seats or firearm components where manufacturers want an attractive surface finish.

Nylon 66 has a higher melting point and is usually more durable than Nylon 6, so it’s a good choice for high-performing products that must withstand heat or wear and tear. That characteristic makes it a popular choice for items such as friction bearings, battery modules, luggage and conveyor belts.

Both Nylon 6 and 66 are used in household items. Nylon 66 tends to be more commonly used to make products like durable carpeting, whereas Nylon 6 is often found in places like the bristles of a cleaning brush.