Rubber Mattress Wooden Slat Foundation: The slatted wooden foundation - allows air flow on the underside of the mattress or the wood slat box. The best foundation for the futons is the wood slat box which has a heavy-duty organic cotton cover over extra-firm support from wide wood slats placed every two inches for maximum coverage. The premium foundation for the natural rubber mattress is the Flexible Slat Foundation, with thinner slats than the basic foundation.  This slat system allows airflow on the underside of your mattress.  Benefits: No toxins or noxious fumes to inhale while sleeping. Sound, supportive box frames that won't crack with age or dryness Features: The manufacturer covers the sides of this foundation with organic quilted cotton and wool to match the mattress.