All minerals, including magnesium, have to be attached to a carrier to be transported into the body. That carrier can be an oxide, malate, citrate or one of the many other carriers. For your body to be able to absorb the magnesium, it needs to “unplug” the magnesium from the carrier (e.g. citrate) and then “plug” into your body.
For a mineral to be ionic, it means there are ions readily available to attach to a carrier. An analogy would be like the exposed prongs of an electrical plug. I.e. the prongs are exposed, looking for a new home.
Some plugs are hard to pull out, especially if it is a twist lock. In the mineral world, this would represent a strong bond. Magnesium citrate is one of the easier salts to unplug, whereas magnesium oxide is one of the hardest to unplug. (That is why magnesium oxide is not absorbable.)
In the mineral world, what ionizes the mineral, is acid. In order for your body to unplug the magnesium from the citrate, so your body can utilize it, it relies on the acid in your stomach.
MAG365 is made from two ingredients; magnesium carbonate and citric acid. When you add hot water, the citric acid combines with the magnesium carbonate and the carbonate leaves (fizzes) and what you are left with is an ionic solution of magnesium citrate. This means that all the magnesium is in the solution, “unplugged” from the citrate and is ready to plug into your body.
Though you can find other products of magnesium citrate, either bulk, (in a jar) or in capsule form, they are not as bioavailable as MAG365 since they depend on your stomach acid to ionise the magnesium. Remember too, as we get older, we produce less stomach acid. The fact that magnesium citrate is one of the most bioavailable forms may be true, but unless it is ionised, it will not be effective.
MAG365 is an ionic magnesium citrate, manufactured in your mug, ready to be absorbed.