Water Softener Topic 11/11: Softener resin, what is it and how to choose?

Thank you for your overwhelming support to series of my posts relating to various aspects of water softener systems. I am penning this in response to some users requesting to understand importance of resin as it relates to water softener and how (if possible) to revive old softeners. I have received at least 3-4 requests in the past one week on this topic and thought, I would share what I know for the benefit of anyone owning a water softener or planning to have one.

Resin is an integral part of the water softening system. Given this, let us try to understand what are they? In simple terms they are spheres typically made of numerous Polystyrene (synthetic hydrocarbon polymer of styrene) strands and wrapped in a crisscross manner allowing water to passthrough the negatively charged (anion) carboxylate which gets attached to positively charged (cation) sodium. The intersection of strands is called a crosslink and a resin contains several number of crosslinks.

As the hardwater (water containing calcium and magnesium) enters into the resin tank, it goes through these bead