Synthetic fabric turning to dust

A friend has a jacket manufactured from some synthetic fabric in 1964. It was originally a steel blue color, but it is decaying into dark brown powder. It is a stretchy weave textile, but I don’t think it’s polyester, because I’ve seen racks of polyester neckties from the 1960s and 1970s (my dad’s) that haven’t decayed one bit.

Anyone have a guess on what fabric it is, and if anything can be done to stop the decay? It has a great sentimental value.

Oops, sorry, I accidentally resubmitted this thread. Please ignore and/or delete this one.