This product is designed to lay under a foam or inner-spring mattress. It is approx. 10mm thick. It is non-woolen, non-organic spring-like suspension designed to allow air to circulate between your mattress and the baseboard. The airflow enables the mattress to remain dry, preventing mould stains, moisture damp and musty smells, etc. It also keeps the baseboard dry and clean smelling. It does not sag. It is a fantastic product, equally at home in a boat, caravan, 4WD or RV. It uses up almost no room.