They are both glass fibres in phenolic resin, but in textolite glas fibres are woven to a textile like mesh, while in fiberglass they are placed "at random". In tank armor version I am pretty sure they are in 1st form (at least it looked so on the cutaway).
AG-4 isn't glass textolite, it's fiberglass.
Which subvariant of AG-4 was used in tank armor anyway?
Yes, that's right, the glass fibers are woven into sheets, so that makes it a glass textolite and not a fiberglass. I have heard the term "steklotekstolit" many times in reference to the T-72, so it simply cannot be fiberglass, so no AG-4. I read that it is probably KAST-V.