An excellent way to develop a line of rackets, IMO. Back in the '70s through '90s, quite a few companies took advantage of this techinque...allowing some interchangeability of bumpers/grommets, etc. Head, Wimbledon, Wilson, Chris and others had a 'progression' of materials, stiffness, price throughout their lines while using the same mold for the various layups. It was very common when a brand wanted to offer SMUs to large retailers...same mold, different cosmetics and sometimes, different compositions. Brilliant in its simplicity.
Here's just an intro on S2 fiberglass:
"S-2 Glass® Fiber Family of products offer a combination of six vital enhanced properties critical for your demanding applications. Compared to conventional glass fiber, the ehnanced properties of S-2 Glass® fibers result in better weight performance, and when compared to aramid and carbon, they deliver better cost performance."
There's an eighteen page brochure...IF you are trying to fall asleep!
http://www.google.com/url?sa=t&sour...Nyg5ZBsFg&sig2=NVpSCOkI9mwwPrdO14eJoQ&cad=rja