Joseph Gwinn fired this volley in news:joegwinn-
:

What is the roving made of?

Joe, it's a very slightly twisted bundle of jute and cotton yarns and
cotton bias tape. VERY stretchy. Over the processing length of the
machine (about 80'), it will undergo about a foot of stretch at 20lbf
tension, and recover virtually all of it if released.

The tensioning requirement is not for the spooling -- the takeup spool
merely provides the necessary process tension. As the tension varies,
the overwrap of bias tape changes its spiral angle (from sideways
"yanking" of the roving in the wrapping area), and becomes uneven in
overlap and lay.

Only under fairly strict constant tension will the overwrap be as uniform
as customers demand for the product.

Stiff and light -- High resonant frequency.

LLoyd