Ribbed Caps are the basic closure in the packaging business. The Ribbed Cap is a threaded closure with an uninterrupted spiral mechanism. This provides the user the ability to easily seal and reseal the container. The ribbed sided design provides easy gripping for the user to twist on and off. This cap has a flat matte top, which easily allows for labeling.  Foam liners tend to be used in many common caps.  A foam liner, as it name implies, has a thin low density foam ring, which is sandwiched between two layers of low density polyethylene (LDPE) film. When chemical resistance or low moisture transmission is important, you will want to select a Foam Liner. You will also find that these liners protect from odor transmission and do not impact the taste of food products in the container.  Very often you will see these referred to as F-217 or Sureseal liners, which is an industry trade name.