The L2210WHF2 is a white urea 43-400 smooth skirt lid with foam liner. This closure includes a foam liner, which will create an airtight seal when the lid is securely screwed on to the container. This lid is made of urea, an industrial grade, highly rigid, plastic with a good resistance to solvents and high temperatures. This closure fits a container with a 43-400 neck finish. The first number refers to the diameter of the container's opening (in mm). The second number refers to the thread/style/depth of the closure's skirt. Please read 5 seals and how they make perfect liners for your container for more information on liner types.