Disposable pull-on diaper

A pull-on disposable diaper comprising:

• an absorbent structure having:
• a liquid-pervious topsheet;
• a liquid-impervious backsheet;
• and
• a liquid-absorbent core disposed between the liquid-pervious topsheet and the liquid-impervious backsheet so as to define a front body region for contacting a wearer's belly, a rear body region for contacting a wearer's back, and a crotch region extending between said front and rear body regions;
• and
• a trunks-shaped cover at least partially covering said absorbent structure,
• said absorbent structure being folded upon itself along said crotch region with said topsheet inside so as to have opposite side edges extending in a vertical direction of the diaper and longitudinal ends of said front and rear body regions extending between said opposite edges,
• said trunks-shaped cover comprising:
• a first sheet for covering at least a portion of said front body region and a front side of said crotch region;
• and
• a second sheet for covering at least a portion of said rear body region and a rear side of said crotch, said first and second sheets respectively having opposite side edges extending in said vertical direction of the diaper and upper and lower edges extending transversely of the diaper, said first and second sheets being bonded to each other along their opposite side edges and transversely middle zones of their lower edges to define a trunks-shape, and said first and second sheets having respective inner surfaces of their upper edges bonded to front and rear sides of said absorbent structure respectively,
• at least one of said first and second sheets having a pair of pleats extending the entire vertical length of the trunks and symmetrically with respect to a center line dividing a width of the diaper in two, said pair of pleats having a Z-shaped cross-section and inverted Z-shaped cross-section, respectively.