The sides of the box are designed to be high enough to safely contain the puppies, yet low enough to allow the mother to enter and leave comfortably, with consideration given to her protruding mammary glands. Alternatively, the box is provisioned with a doorway with adjustable height for the same purpose. The bottom of the box may or may not have a floor and may be lined with specially designed "whelping pads," or layers of newspaper (or fabric) to provide insulation from cold floors and to absorb fluids. Fabric covers or partial covers are often used on top to provide a "den-like" environment for the mother. Full covers may be used to prevent puppies from escaping.
