A plantar insole has bearing areas (6, 7, 8, 9) of the main surface which are provided with a rigidity or hardness which are less with respect to other areas (10-13) of the main surface. These areas (6-9) are arranged under the major bearing areas of a foot, i.e. under toes, under the metatarsal heads, under the heel and under the external bearing area of the foot, making it possible to attain a compromise between the necessity of an impact absorption and stabilization of the foot in a shoe. The insole may be adapted to any type of footwear.