Povidone K90 has a significantly higher molecular weight and viscosity compared to Povidone K30, meaning K90 is better suited for applications requiring high viscosity like thick gels or strong hold hair products, while K30 is preferred for lower viscosity applications like sprays or liquids with a lighter hold; both are used as binders and stabilizers in pharmaceutical and cosmetic formulations, but K90 generally has a stronger binding capacity due to its higher molecular weight.