Mainline Cork Dust Pop Ups are highly buoyant due to the cork dust used and will stay popped up for a very long time. As with normal pop ups, once you pierce their outer skin you allow water to soak into the pop up and make it heavier, which then leads to it sinking. But with cork, the water doesn't soak into it, hence keeping it buoyant for longer. Also in cork dust pop ups, they can use the same base mix ad your bait baits but standard pop ups are only a pop up mix that has been flavoured to smell like you bait.