Have you heard of crystalline vs. amorphous types? Most of us don’t know the difference between the two, but in the biochemistry world, it makes a really BIG difference to stability. 

Crystalline salt molecules are considered extremely stable whereas amorphous salt molecules are known to be much less stable because of the higher exposure to oxygen. Check out the picture below showing a representation of the structure differences. It makes it easy to see why the crystalline molecule would be more stable than the amorphous (in the holes is oxygen - and therefore more oxidation and destabilization).

With the unique C crystal structure, Magnafolate can well isolate oxygen, so it can be stable for 3 years at the room temperature. Actually, great stability for Magnafolate also means much purer because it is not easier to degrade and bring harmful impurities.