There was a time when you could actually specify THHN or THWN, but not anymore. All you will ever see today is a combo. Maybe what you saw was THHN from the 1960's?
Sunlight will do quite a job on anything. The outer nylon jacket cracks, exposing the underlying base color.
THHN in the 1960's????? From what I understand it was rolled out in the 70's .
