An article of footwear includes a flexible cover shaped to envelope at least a portion of a wearer's foot. The cover has a sole region with inner and outer surfaces, the inner surface positioned to face the sole of the wearer's foot and the outer surface positioned to face in an opposite direction. The cover also has a plurality of apertures formed in the sole region. The article further includes a removable outsole nested within the cover. The outsole has an upper surface positioned to face the sole of the wearer's foot, a lower surface facing the inner surface of the cover sole region, and a plurality of lugs on the lower surface which protrude into the plurality of apertures.