Yuri:

You are answering a question that was not asked. Your answer is excellent if
the question we Is it necessary, when calculating element length, to
consider the type of wire used?

If you calculate based on insulated wire and then build it out of bare wire,
it ain't going to work well either.

Assuming one calculates for whatever radiating thingy one is using, it makes
little difference whether that thingy is bare or insulated.

Paul AB0SI

The question was:
"What are pros and cons of using insulated twisted pair wire for wire
antenna projects? (its what I have handy) Comments invited."

Lacking more specific question (didn't say white kind of "wire antenna
projects" resonant or random length), I pointed out "cons" - the effect of
insulation on calculation and modeling the antenna's physical length vs.
electrical. 5% shortening from insulation makes difference if you end up in 10m
ham band or 11m CB band, that is 1.4 MHz difference and that IS significant.

Inquirer can decide for himself if it is important for his case (making
resonant antennas) or not (non resonant, long wire antennas).

If I offended anybody's insulation, then I am sorry :-)

Yuri, K3BU