Difference between S-glass and E-glass?

What is the difference between S-glass and E-glass? P-Net and Google searches have revealed nothing.

I know what glass cloth and glass mat are, but mentions of S and E-glass are confounding. Obviously I’m missing a critical key word.



I got this from a search

Yes, that is my source. Although
I first learned about S-glass from Charlie Walbridge’s Boatbuilder’s Manual.

S-glass makes an excellent material for the outer two layers of a composite boat. It is stiff enough to give a hull good rigidity, but it is also more resistant to breaking than E-glass, and being harder, it resists the effects of dragging over rocks.

On my whitewater boats with S-glass exterior, small breaks may appear in the top layer, but seldom go deeper. Often I need to do only minor surface preparation, and then put on a single or two layer S-glass patch. My boats are not gelcoated, so it is very easy to see any damage and deal with it.

S glass is stronger
some say about 30%. I’m just repeating info, so not sure if it’s fact. It’s also more costly. That info cams from an aerospace composite engineer.

I am having a Bjorn Thomasson Black Pearl built right now and the builder (Dan Cauouette) is utilizing S-glass on it. He has stated that this glass is lighter and quite strong and i asked for it to save weight on my 18.5ft boat. I just got an email from Dan tonight, and he just weighed my boat in at 26lbs with all glassing done. He is thinking the final boat weight should be about 29-30lbs maximum and yet be a strong build. Cool…

To read up on the build - here is the blog where Dan states what weights of Sglass he uses and where and why.




your google must be broken
found this on the very first search.

Imagine fiberglass that will flex longer without breaking and will be more resistant to abrasion. For s&g kayak construction I made a few dozen test panels with 4mm ply. Comparing two panels, one with 4oz e-glass on both sides, one with 4oz s-glass on both sides. Put the 6"x6" panel against a step with the long grain on both sides sideways (weak direction) and slowly stepped on it. The e-glass panel broke in half with wood splinters defining the breaks. The s-glass panel bent into an open U shape with whitening of the fibers and damage to the wood but no open fractures through the fiberglass.

But 6oz e-glass was stronger than 4oz s-glass and cheaper.

Comparing 6oz s-glass to 6oz e-glass the wood fractured on both but the wood was confined within the fibers.

With punctures through the wood the s-glass panels had whitening of the fibers for 1/2 the distance from the hole than the e-glass. With the e-glass the wood fractures extended beyond the hole with right angle fractures in the glass about twice the distance as the s-glass.

It’s a better glass like vinylester is a better resin than polyester.


Search is fine. My brain however…
I had it in my head that “S” or “E” designated a type of weave and was using the wrong key words.

Thanks for the info; makes perfect sense now.