craftgrrl | Need help identifying something.

I'm (still) trying to make a backpack. I finally got around to buying everything. But, I appear to be missing something. I took a backpack apart, and there was a think black ribbon-like thing around all the sewn edges. I think it's supposed to protect the edges of the material as well as help make the bag waterproof. What ever it is, it's very flexible, about 3/4 in wide, looks like it's got a diamond pattern on it (the diamonds are recessed so it's thinner in parts), and can be torn by hand.

It looks like it might be piping?

I bought nylon webbing on ebay. It's obviously wrong. Far too rigid. I think it's for straps?

-edit.

Right sorry. It's on the INSIDE of the backpack.

-edit2

I've ordered bias tape. Even if it isn't the same thing I had, it should work.