DD,

I relied on memory, which is occasionally hazardous. I don't recall which, S glass or E glass is the slightly higher modulus. Fenwick gave the higher modulus one the trade name Fenglass. I don't think there was any different production process. Wrapping the higher modulus fabric on the same mandrel produced an ever so slightly lighter rod blank with greater strength (modulus being a measure of tensile strength) and faster action.

When graphite was used to fabricate rod blanks, the big deal to overcome was its brittleness compared to fiberglass. That has continued with each new generation of graphite fiber, they are lighter and stronger, but also more brittle. Manufacturers have done a fantastic job of making graphite fiber more suitable to rod building, but that inherent brittleness, as much as the sporting goods prestige price wars, led to long-term, lifetime, and unconditional rod warranties. Before that, a new rod carried a limited warranty against defective materials and workmanship, and that was the extent of it. But we had to work really hard to break fiberglass rods, comparatively speaking.

Sg