I have some on order to check it out. My theory is a lot of salt and HD additive to make the core, but the bait weighs 1/2 oz and the core is only 3" long. http://www.landbigfish.com/Keitech/Keitech-Salty-Core-Tubes.cfm
I'm not interested in duplicating this tube bait but the concept is intruiging. It could create some options if a heavy core section were added to a creature bait, magnum lizard or maybe just the center of a wacky worm.
Of course there are other time-proven ways to imbed weight in a soft bait to get it to "back up" on the fall. Don't know if it is a better mousetrap, but it is different.