11mm Snap Top Caps are made of high quality polypropylene, Caps have the profile of a crimp or snap closure for compatibility with robotic autosamplers, Pre-assembled septa reduces the chance of contamination during sample preparation, while saving sample preparation time in the lab.Snap caps provide a secure seal, minimizing evaporation even with volatile samples, The audible click ensures that a secure seal has been formed and the cap is properly applied.