The opaque closures protect contents from UV light when used with opaque bottles. Reduce chance of cross contamination Opaque white, amber, green, red, and blue closures protect contents from UV light when used with opaque Nalgene bottles One-piece, linerless, with integrally molded seal ring Fit Nalgene narrow-mouth 8, 15, 30, 60mL bottles Well-defined closure knurl makes gripping and capping easy Guarantee leakproof, when used with Nalgene narrow-mouth bottlesMeer tonenMinder tonen