The Petnap Disposable Whelping Box is constructed from robust, double-walled corrugated cardboard, making it ideal for hygiene and convenience. These boxes are designed for single use to prevent cross-contamination between litters. Each box comes with a water-resistant cardboard base and includes three wooden puppy rails made from 21mm dowel. These rails create a safe zone for puppies, protecting them from being accidentally rolled on by the mother. The box features a fold-down entry flap and is shipped flat-packed to minimize packaging. To determine the correct size, measure the mother dog from nose to the base of her tail, adding four inches if puppy rails will be used. Choose the box size that allows her to lie down comfortably along one side, typically the next size up from your measurement.