Vapor Trail Bowstring Elite Impulse 31 57 in Green. These by Vapor Trail utilize a material called VTX that is a patented material that gives added strength and durability to the bow string. The Vapor Trail Elite Impulse Bowstring also has Precision Winding which reduces abrasion and produces less creep. Combine all this with quality materials and workmanship and you get a premium bow string that performs for years to come. For a high quality product at an economical cost use the Vapor Trail Elite Impulse Compound Bow String. Package Contents: Vapor Trail Bowstring Elite Impulse Vapor Trail 79422: Bowstring Elite Impulse 31 57 in Green