Abstract: An injection moulded sole (10) has an upper ungrooved portion (2) and a lower tread portion (4). At least two, continuous, undulating S-shaped grooves (6) extend generally longitudinally of the tread portion between the toe and heel ends thereof, and a plurality of grooves extending generally transversely intersect the longitudinally extending undulating grooves. The grooves have a minimum depth of about 5 mm and define individual separated tread areas (28) which can be moved apart during flexing of the sole (10). The flexibility of the sole is such that when it is incorporated in footwear, it does not restrict rolling movements of the foot when walking so that a gait can be adopted which is akin to barefoot walking.