Hello
Pro Polymer is electrolyte resistant, works under a wider pH range
Ultrez 21 is less electrolyte resistant and works under The pH is narrower. If the formula is a general gel, the pH is higher than 4.8 can be used.
Ultrez 21 , it is more economical if the formulation contains an active electrolyte or is difficult to stabilize, or if the formula is low in pH, only
Pro Polymer Only it can work.