Progressive Formaldehyde Free Le Pro 300ml The Le Prö Cosmetics Organic Single Pass Treatment Mask acts on the strands as a whole, nourishing them from the inside out and ensuring aligned, shiny, frizz-free and healthy hair as a result. Its formula was developed with natural and organic active ingredients, which bring greater benefits to the hair and are also 100% of plant origin, ensuring healthier hair at the end of the treatment.