FF or dacron, how do you tell.

[Changeling]

I have never paid any attention to what kind of string I was using till i started reading the posts on this web site.
Question: I have 2 bow strings that are a few years old, is there some way I can tell if they are FF or what through describing them here or is it best left to an expert like Chad? Both are brand new.

Changeling

[BobCo19-65]

You may want to take a mic to it. I believe B-50 (Dacron) is .018 diameter, DF97 is .015.

I just don't think you could tell. Way too close except breaking strength.

[Wingbone]

If stretches or has stretched at all its dacron.