These Oxygen Absorbing beer bottle caps have a special liner that absorbs oxygen in the bottle's head space. This helps reduce the oxidation that happens during the bottling process, keeps your home brewed beer tasting fresher, and can extend its shelf life.
Important to note: It is recommended that you only sanitize as many caps as you'll require at the time of bottling. The oxygen-absorbing agent is activated when the cap gets wet. If wetted caps are saved for later use, they'll still function as a normal cap, but the oxygen absorbing agent may be depleted.