Cationic guar gum is an anti-static and conditioning agent which improves hair combability and shine.
Cationic guar gum is derived from the natural guar gum, a thickening substance extracted from the Cyamopsis tetragonoloba seeds. So why is this ingredient classed as a synthetic? In simple words, the natural gum is modified to be charged with positive ions, which will be attracted to the negative charge of the hair and change it into a neutral charge (old chemistry lessons memories are coming back?), resulting in light and flat hair, easier to brush. This anti-static effect is at the base of all conditioners.
Transformed guar gum also shares thickening properties with the natural one, helping to control the viscosity of a product. It is water-soluble and forms a shiny and silky film on hair, conditioning the hair until the next shampoo.