Our whole kennel facility is concrete and cinder block construction. In our experience, that is the only material that is able to be consistently cleaned while giving us decades of service life. Other materials are subject to degradation over the years by chewing etc. Also, any porous materials such as wood are subject to retaining smell and disease. The outdoor exercise pens are heated concrete as well to facilitate cleaning all year including the winter months. The warm concrete has an added benefit of keeping the dogs feet warm in the winter while outside running around.