the reason I suggest it is that I made a bunch of test panels with 4oz e-glass, 4oz s-glas, 6oz e-glass, 5oz polyester,2" 9oz unidirectional carbon tape, 2" polyester tape and 1 1/2" 5oz kevlar tape.

The funny part about the s-glass panels is how it broke. I put the 6"x6" panels on the step and pressed with my foot until it broke. With 4oz e-glass on both sides it bent and broke completely with fibers on both sides broken completely and the wood shattered. With 6oz e-glass the damage was similar but it took a lot more effort to break it. With 4oz s-glass the panel bent into a c shape without fracturing. The threads were all whitened on both sides and the wood was delaminated on the inside but there were no shards of wood breaking through the glass. I also did some stabbing through the panels with a big screwdriver. The e-glass fractures along the direction of the fibers and underlying wood grain. With the s-glass the fractures extend for about 1/2 the distance and in more of a scattered spider pattern, not straight along the fibers.

Regarding abrasion resistance what I did was pretty crude, simply scraping the point of utility knife back and forth across the surface of the 4oz cloth until I wore through it. The s-glass took more time and effort to wear through than the e-glass. The 3.25oz fineweave e-glass was even easier to wear through than the 4oz regular weave.

If you are thinking of putting on two or three fill coats of this goop you'd get a LOT more impact durability with a layer of 4oz s-glass within it. If you wanted the least amount of goop and weight a thin layer of 3.25oz fine weave e-glass would still provide more impact durability than just slippery fill coats.

To my mind the slippery stuff makes sense if you have to drag the empty kayak over things repeatedly, if you are concerned about you and the kayak sliding over rocks with your body weight and wave action pressing down as you slide over rocks then extra glass or s-glass under the slippery goop makes sense.