Nylon 6-66, also referred to as PA6, PA66,Polyamide resin, is a type of nylon. Nylon comes in many types, the two most common for textile and plastics industries are: nylon 6 and nylon 6,6.
Nylon 6,6 has a melting point of 265°C, high for a synthetic fiber’ this fact makes it resistant to heat and friction and enables it to withstand heat-setting for twist retention. Its long molecular chain results in more sites for hydrogen bonds, creating chemical “springs”, making it very resilient; it has
a dense structure with small, evenly spaced pores. This means that nylon 6,6 is difficult to dye, but once dyed it has superior colorfastness and is less susceptible to fading from sunlight and ozone and to yellowing from nitrous oxide.