The L350b is a black lid made from polypropylene (PP). The lid fits containers with a neck finish of 24-400. The lid includes an F217 liner which will create an air-tight seal when the lid is securely screwed on. This lid is child-resistant making it ideal for packaging pills or other potentially hazardous products. Please read 5 seals and how they make perfect liners for your container for more information on liner types.