Firm flat surfaces have little airflow underneath, so body heat and room-temperature differences can leave moisture at the base. Turn and stand the futon to ventilate regularly, and in humid conditions pair it with a moisture pad; if you find the underside damp, dry it before storing or reusing. Damp ground, grass, tent floors, and persistently wet surfaces are unsuitable for direct use.
For buyers researching shikibuton, shikifuton or a Japanese floor mattress, the key point is how this bedding is used: on a firm, ventilated surface, folded away when needed, and cared for as part of everyday Japanese living.