Harelines Hard as Hull Penetrator Head Cement is designed to lock materials in at their core. This head cement can be used for nearly every type of fly, and its a head cement that you can use every step in the fly should you want a bombproof pattern. Harelines Hard as Hull Penetrator Head Cement is perfect for coating the finishing wraps of a fly, applying them onto a wingcase for extra strength, or locking materials in at the core. A truly versatile head cement, youll find that Hard as Hull Penetrator Head Cement brings long-term strength to every fly you tie.