what's this cloth doing in my surfboard?

 Hello all..... I've just started some repairs to a friends board and came across something I'm unsure about. It is a "Graphlite"  shaped by

M. Perry. About  6'5" single fin, really narrow tail and monster thick! I didn't realize till the grinder started spinning that its got a carbon

fiber(?) strip about an inch wide down the stringer on both sides, paint is on top of the glassing. BUT the cloth I grind down to is

a yellow color and doesn't sand smooth. It feels more like canvas or something. What the heck is this stuff? Kevlar? Burlap?

 Any insight would be great.... and of course how do I make repairs? It needs tail and nose repair, a couple holes filled and a new fin.

Thanks.......

you have any pictures?

 

Sounds like Kevlar (photo’s could help to be sure)

 

Just repair it with fibreglass like you normally do. But use epoxy, because that is almost certainly used if it has carbon and kevlar.