Right here summes it up.
http://jas-townsend.com/product_info.php?products_id=665
It's not just for sewing though,makes a great wrap too.My brother made obsidian arrow heads & the occasional knife blade & used the artificial sinew on the knives,looked great.

SYKCO JYD#112
It's better to have it & not need it, than to need it & not have it.