An article of footwear includes a flexible insole having a ball portion arranged below the ball of the user's foot, the bottom surface of the ball portion containing a plurality of transversely-arranged longitudinally-spaced flex grooves that define therebetween a plurality of flex bars which impart a desired degree of flexibility to the insole. A longitudinally-extending shank slot is provided beneath the arch portion of the insole member for receiving a bowed semi-rigid shank member that supports the arch portion of the user's foot. An annular sealing gasket may be provided in a sealing channel that extends around the flex grooves, flex bars and shank slot, thereby to prevent moisture from entering the depressions in the bottom of the insole member.