An article configured for placement on a foot of a human wearer, comprising: a flexible cover shaped to generally surround a foot below an ankle of the wearer, the cover including: a sole region having opposing inner and outer surfaces, the inner surface positioned to face the sole of the foot; an upper region connected to the sole region and forming a void configured to receive the foot of the human wearer; and a plurality of apertures formed in the sole region and a plurality of apertures formed in the upper region; and a removable outsole nested within the cover and including: opposing upper and lower surfaces, the lower surface facing the inner surface of the sole region of the flexible cover, and a plurality of lugs on the lower surface protruding into the plurality of apertures formed in the sole region, wherein the plurality of lugs and the plurality of apertures formed in the sole region are relatively sized and shaped so that edges of said apertures conform to and frictionally retain said lugs, wherein the plurality of apertures formed in the sole region and the plurality of apertures formed in the upper region have a diameter of from 5.5 mm to 16.5 mm, and wherein the plurality of lugs includes also a limited number of lugs that protrude through the plurality of apertures formed in the sole region and the plurality of apertures formed in the upper region on or near an interface of the sole region and the upper region of the cover. a flexible cover shaped to generally surround a foot below an ankle of the wearer, the cover including: a sole region having opposing inner and outer surfaces, the inner surface positioned to face the sole of the foot; an upper region connected to the sole region and forming a void configured to receive the foot of the human wearer; and a plurality of apertures formed in the sole region and a plurality of apertures formed in the upper region; and a sole region having opposing inner and outer surfaces, the inner surface positioned to face the sole of the foot; an upper region connected to the sole region and forming a void configured to receive the foot of the human wearer; and a plurality of apertures formed in the sole region and a plurality of apertures formed in the upper region; and a removable outsole nested within the cover and including: opposing upper and lower surfaces, the lower surface facing the inner surface of the sole region of the flexible cover, and a plurality of lugs on the lower surface protruding into the plurality of apertures formed in the sole region, opposing upper and lower surfaces, the lower surface facing the inner surface of the sole region of the flexible cover, and a plurality of lugs on the lower surface protruding into the plurality of apertures formed in the sole region, wherein the plurality of lugs and the plurality of apertures formed in the sole region are relatively sized and shaped so that edges of said apertures conform to and frictionally retain said lugs, wherein the plurality of apertures formed in the sole region and the plurality of apertures formed in the upper region have a diameter of from 5.5 mm to 16.5 mm, and wherein the plurality of lugs includes also a limited number of lugs that protrude through the plurality of apertures formed in the sole region and the plurality of apertures formed in the upper region on or near an interface of the sole region and the upper region of the cover.