A corner sleeve with a hammock-like cushioning structure includes first and second air-column sides and a bottom air-column side. The inner surfaces of the first and second air-column sides are bonded together at a lateral end, except in the vicinity of the bottom air-column side, such that a deformable opening is formed at an end corner of the corner sleeve by the unbonded parts of the inner surfaces of the first and second air-column sides at the lateral end. The air columns of the three air-column sides that form the deformable opening define a cushioning side at the end corner of the corner sleeve. A hammock-like enclosing film extends between the first and second air-column sides without contact with the bottom air-column side. An end corner of an object to be packed can be wrapped between the first, second, and bottom air-column sides and the cushioning side for enhanced protection.