There are 2 types of stretch cord. One is an elastic based cord such as Elasticity - which has a flexible polyurethane coating to protect it from the elements and breakage.. The other is a fiber based cord such as Opelon and Elonga - often called stretchy floss. They are constructed with multiple stretchy fibers that offer superior drape especially with light weight beads. Always pre-stretch your cord before use. To finish tie a surgeon's double overhand knot and secure with a dab of glue. All stretch cord can break if exposed to sharp edges, such as crystal or natural stone. Wherever possible use a reamer to smooth edges.