Cycle-4 (Soft Sour) softens and fluffs all fabrics and contributes to "wrinkle free" results. Cycle-4 eliminates static cling and reduces extractor time. Cycle-4, when used in proper concentration, neutralizes residual alkalinity which is critical where soft, irritation-free garments and bed linens are needed. Cycle-4 contains optical brighteners and is safe on natural and synthetic fabrics