: WHat is the difference between "E" and "S" glass, and
: which do I want to use for my OI?

S glass is stronger, and more expensive. E-glass is more than strong enough, and you can sometimes find excellent sales.

As I undrstand it, E glass was so named because of its excellent electrical insulating properties while the S glass was specifically designed for higher strength.

"Glass" is a mixture of silicon and other ingredients which will affect the many attributes of the final product. Think of the silicon-based sand which is used in making glass as being a material much like wheat, whcih an be ground into flour, and that flour an be used in millions of recipes to give you pretzels, pizza crusts, cakes, breads, gravies, and wallpaper paste. In the same way the various glass recipes cna be used to turn out optical glass and crystal as well as the spun glass wool used for insulation.

S glass cloth starts with a recipe for glass that is stronger than the glass used in E-glass cloth. After that the material is made in the same way.

With both materials the strength of the final product has a lot to do with the volume (or weight) of glass in that product. In most cases a 4 ounce cloth is going to be stronger than a 2 ounce cloth, and weaker than a 6 ounce cloth. when weight is critical it might be necessary to substitute a lighter weight of a stronger material, say, a piece of 3 ounce S-cloth for 4 ounce E-cloth.

S-cloth is frequently overlooked by our group. There is nothing wrong with it but the price. besides, we don't generally use so much cloth that we would appreiate the difference. When greater strength at lighter weight is required people will frequently shift to carbon fiber cloth rather than experiment with a variation in glass cloth.

The amount of pressure on the hull of most kayaks is under 1 pound per square inch. The strength of E-glass is measured in the hundreds (and thousands?) of pounds per square inch. With such an enormous difference between the needs of the builder and the properties of this material I don't think it is necessary to look for something even stronger. But, of course some people always do.

PGJ