This 3.13 mm (1/8") shock cord made from braided Kevlar® fibres, reputably stronger than steel, is flexible and heat resistant, thus ideal to cope with the scorching heat of the rocket engine's ejection charge. We recommend the shock cord in your rocket be a minimum of three times the length of the model. Longer is better, as this helps prevent zippering (tearing of the airframe tube by the cord cutting into the body tube material. Price is per metre.