fiberglass cloth weigth

here’s the question: if i’ve got 200 square feet of fiberglass cloth that’s 4 ounce cloth, and a second roll that’s the same size but is 2 ounce cloth, how much weight difference? a few ounces? more?

Raises an interesting question.
Six ounce e-glass and six ounce Kevlar weigh the same, per yard. Resin absorption depends mainly on the weave. Perhaps some people think that boats made with Kevlar are lighter because Kevlar is lighter. If they are lighter, it has to do with fewer cloth layers needed to achieve a certain objective.

A 5/4 hull/deck layup in all Kevlar might be a nightmare. Replace the outer two layers with a couple of layers of S-glass, weighing exactly the same per yard, and you get a fairly stiff boat with some capacity to absorb impact.

Resin content of hand laminated fabric; carbon, Kevlar or glass, runs ~55% or more.

So 2oz glass weighs 4oz+ resinated. 4oz glass weighs 8oz+ per sq yard.

The twice heavier fabric is significantly stronger.

Wet bagging drops resin % somewhat. Infusion drops resin content to ~46%; use of prepreg yields ~ 44% resin content.