Leak-proof cap for drinking bottles. The Sigg Tritan Adapter is a great addition for all Sigg drinking bottles with a wide mouth opening. This allows any Sigg cap designed for narrow mouth bottles to be used on all wide mouth drinking bottles. Additionally, the practical screw cap remains sealed at all times, ensuring that the drinking bottle is guaranteed to be leak-proof. The screw cap contains no harmful substances, including phthalates or estrogen-active substances.