Nylon 6 is made from a monomer that has 6 carbon atoms. It is known for good melt strength, which makes it an excellent candidate for extrusion, keeping processing in consideration. Its chemical resistance is also fairly high.
Nylon 6,6 is made from two different monomers that each have 6 carbon atoms. It retains the same general properties of nylon, but with finely tuned changes. For example, Nylon 6,6 has more brittle fracture behavior than Nylon 12 when below room temperature, but has better high temperature resistance than Nylon 6.
Nylon 11 is made from a monomer that contains an 11-carbon-atom backbone. Its properties tend to be mid-range for nylon, and thus, can be used for many multipurpose applications.
Nylon 12 is made from a monomer that contains a 12-carbon-atom backbone. Nylon 12 typically has the lowest water adsorption of nylons, offering the least amount of heat and moisture distortion of the nylon family.
Pebax® is the trade name for the polymer typically known as PEBA, or polyether-block-amide. This is a softer alternative to nylons. Pebaxes are typically used for long catheters meant to navigate the circulatory system because they soften nicely at body temperature, improving the comfort of the patient over nylon, while still retaining some of the wear resistance of nylon due to their blocky amide structure.
Different Pebax durometers are sometimes used in the same catheter. A softer durometer would be used on the distal end to provide ease of navigation, with a harder durometer on the proximal end to provide strength and support to push-through.