A wide variety for just about any application. From elastic to Kevlar to Tubular Nylon. Elastic is great for light weight (for 1-24oz weight rockets) applications and can stretch to 175% of length. Kevlar (for 1-24oz rockets) has 220# tensile strength and is a great alternate choice for elastic. It is thinner in size so be mindful of zippering! Our new 3/16″ ( 2-32oz rockets) tubular nylon is an excellent choice (375# tensile strength) to replace either elastic or kevlar and has loops sewn into the ends. Flat nylon (1-7 pound rockets) comes in with a 900# tensile strength and has loops sewn in for easy attachment or replacement. Great for almost all high-power flights. Tubular Nylon is the strongest we offer with over 2,200# Tensile rating for Extreme application, it has loops sewn into the ends for easy attachment or to replace your existing cord!