.013" Medium Thickness. Gossamer Floss is an incredibly stretchy, thin fiber cording - sometimes called Opelon. It is an amazingly strong, stretchy, multiple fiber cording that looks like dental floss, but has an amazing elastic quality. It threads through 10/0 seed beads and size 3 & 4 crystals with a collapsible needle. There is no need to use crimps (they may actually fray the material) simply tie a knot to secure.