Can nylon 6 and nylon 66 be used interchangeably?
In many cases these two nylons can be substituted for each other. Each resin, though, has some advantages in particular situations. Nylon 66 has a higher melting point, so the heat distortion temperature is higher than for nylon 6. However, the long-term heat stability of the two resins is similar. Nylon 6 is incompatible with antifreeze solutions, but nylon 66 has long been used in radiator applications. Nylon 66 absorbs less moisture than nylon 6, so the properties after conditioning do not change as much. Nylon 6 is considered to have a better surface quality and higher impact strength.
