Your new litter of puppies will require a lot of care from both the mother dog and her human caretakers. Young puppies need to be kept in clean, safe surroundings where they can develop and mature in a healthy manner. The floor surface that your puppies are living on as they learn to move around can impact the way they develop.
The 3-Week Old Puppy
Three-week-old puppies are just learning how to move around. These puppies have likely noticed the existence of their siblings and mother and are just starting to learn to explore the area you have them living in. They need to be kept in a safe place that they cannot escape from and where the mother can still easily care for them. The flooring of your puppies' enclosure can help enable the puppies to explore or it can hinder their progress.
The best flooring surface for a 3-week-old puppy is sturdy and secure. The flooring should not tip or bend significantly when your puppies are learning to walk on it. It should not have holes that puppy feet can become trapped or caught in, which is why wire cages should not be used for housing small puppies unless a plastic tray is covering the bottom of the cage.
The best surface for your 3-week-old puppies to learn to walk on is a dry, smooth surface that offers some kind of traction. You do not want the flooring to be slick under your puppies paws, because a slick surface will make it harder for your puppies to learn to walk. A non-slip bathmat or other slightly nubby floor cover can help add traction to slippery surfaces.
Three-week-old puppies do not have control of their own elimination habits. Young puppies use the bathroom whenever and wherever the urge strikes them. The surface of your puppies' enclosure absolutely must be washable so that you can periodically clean and disinfect it. Walking around in old feces and urine residue can make your puppies sick.